Wound cleansing apparatus with scaffold

ABSTRACT

An apparatus for cleansing and applying therapy or prophylaxis to wounds, in which irrigant fluid containing a physiologically active material from a reservoir connected to a conformable wound dressing and wound exudate from the dressing are recirculated by a device for moving fluid through a flow path which passes through the dressing and a means for fluid cleansing and back to the dressing. A biodegradable scaffold underlies the dressing on the wound bed to promote tissue growth. The cleansing means (which may be a single-phase, e.g. micro-filtration, system or a two-phase, e.g. dialytic system) removes materials deleterious to wound healing, and the cleansed fluid, still containing materials that are beneficial in promoting wound healing, is returned to the wound bed. The dressing, an assembly comprising the dressing and scaffold, and a method of treatment using the apparatus.

BACKGROUND OF THE INVENTION

The present invention relates to apparatus and a medical wound dressingfor aspirating, irrigating and/or cleansing wounds, and a method oftreating wounds using such apparatus for aspirating, irrigating and/orcleansing wounds.

It relates in particular to such an apparatus, wound dressing and methodthat can be easily applied to a wide variety of, but in particularchronic, wounds, to cleanse them of materials that are deleterious towound healing, whilst retaining materials that are beneficial in sometherapeutic aspect, in particular to wound healing.

Before the present invention, aspirating and/or irrigating apparatustherefor were known, and tended to be used to remove wound exudateduring wound therapy. In known forms of such wound therapy, the offtakefrom the wound, especially when in a highly exuding state, is voided towaste, e.g. to a collection bag.

Materials deleterious to wound healing are removed in this way.

However, materials that are beneficial in promoting wound healing, suchas growth factors, cell matrix components, and other physiologicallyactive• components of the exudate from a wound are lost to the sitewhere they can be potentially of most benefit, i.e. the wound bed, whensuch therapy is applied.

Such known forms of wound dressing and aspiration and/or irrigationtherapy systems often create a wound environment under the dressing thatthus may result in the loss of optimum performance of the body's owntissue healing processes, and slow healing and/or in weak new tissuegrowth that does not have a strong three-dimensional structure adheringwell to and growing from the wound bed. This is a significantdisadvantage, in particular in chronic wounds.

It thus would be desirable to provide a system of therapy which canremove materials deleterious to wound healing from wound exudate, whilstretaining materials that are beneficial in promoting wound healing incontact with the wound bed.

Dialysis is a known method of treating bodily fluids such as blood exvivo, to cleanse them of materials that are deleterious to the bodysystemically. Removal of such materials by contact with the dialysate isthe prime purpose of dialysis, whilst also retaining materials such asblood, cells and proteins. Other materials that may have an additionalpositive therapeutic action are potentially lost to the system throughthe dialysis membrane, which is also permeable to them. The balance ofsuch materials in the bodily fluid in recirculation may thus be furtherdepleted.

It would be desirable to provide a system of therapy which can removematerials deleterious to wound healing from wound exudate, withoutsubstantially diluting materials that are beneficial in promoting woundhealing in contact with the wound bed, and which can continuously supplyand recirculate such materials to the wound simultaneously.

Dialysis for treating bodily fluids is also a systemic therapy, sincethe treated fluid is returned to within the body.

This is in contrast to a topical therapy in which the treated fluid isrecycled outside the body, e.g. to a wound.

Dialysis also requires large amounts either of bodily fluids such asblood or of dialysate, and consequently the relevant devices tend not tobe portable.

Even when in a highly exuding state, chronic wounds produce relativelylittle fluid to be treated compared with internal bodily systems andrelatively little materials that are beneficial in some therapeuticaspect to be retained in the wound and/or its environment.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate at least some of theabovementioned disadvantages of known aspiration and/or irrigationtherapy systems, and to provide a system of therapy which can removematerials deleterious to wound healing from wound exudate, whilstretaining materials that are beneficial in promoting wound healing incontact with the wound bed.

It is a further object of the present invention to obviate at least someof the abovementioned disadvantages of known dialysis systems, and toprovide a system of therapy which can remove materials deleterious towound healing from wound exudate, whilst retaining materials that arebeneficial in promoting wound healing in contact with the wound bed,without affecting the body systemically.

It is a yet further object of the present invention to obviate at leastsome of the abovementioned disadvantages of known dialysis systems, andto provide a system of therapy which can remove materials deleterious towound healing from wound exudate, whilst retaining materials that arebeneficial in promoting wound healing in contact with the wound bed, andis portable.

Vascular supply to, and circulation in, tissue underlying andsurrounding the wound is often compromised. It is a further object ofthe present invention to provide a system of therapy that retains andsupplies therapeutically active amounts of materials that are beneficialin reversing this effect whilst removing deleterious materials, therebypromoting wound healing.

Another known apparatus for wound healing comprises a section ofopen-cell foam configured to be placed over a wound, a flexible tubeinserted into the foam section for attachment to a suction pump, and aflexible polymer sheet overlying the foam section and tubing andconfigured to be adhered to the skin surrounding the wound. It isclaimed that there is potential to stimulate and drive tissue growth inthis way.

A significant disadvantage, in particular in chronic, wounds, is that inuse granulation tissue is drawn into the sponge that lies between thewound film dressing and the wound bed.

This granulation tissue in-growth must necessarily be removed, usuallytraumatically and/or with sharp debridement on dressing change, or hasto be minimised by using non-penetratable wound contact layers.

It thus would be desirable to provide a system of therapy that canobviate the disadvantages of such known therapy systems.

Thus, according to a first aspect of the present invention there isprovided an apparatus for aspirating, irrigating and/or cleansingwounds, characterised in that it comprises:

-   -   a) a fluid flow path, comprising        -   i) a conformable wound dressing, having            -   a backing layer which is capable of forming a relatively                fluid-tight seal or closure over a wound and            -   at least one inlet pipe for connection to a fluid supply                tube, which passes through and/or under the wound-facing                face, and            -   and at least one outlet pipe for connection to a fluid                offtake tube, which passes through and/or under the                wound-facing face,            -   the point at which the or each inlet pipe and the or                each outlet pipe passes through and/or under the                wound-facing face forming a relatively fluid-tight seal                or closure over the wound,            -   at least one inlet pipe being connected to a fluid                recirculation tube, and            -   at least one outlet pipe being connected to a fluid                offtake tube:            -   ii) a means for fluid cleansing having at least one                inlet port connected to a fluid offtake tube and at                least one outlet port connected to a fluid recirculation                tube; and        -   iii) a biodegradable scaffold located under the backing            layer and configured to be placed in contact with a wound            bed in use;    -   b) a fluid reservoir connected by a fluid supply tube to an        integer of the flow path (optionally or as necessary via means        for flow switching between supply and recirculation);    -   c) a device for moving fluid through the wound dressing and        means for fluid cleansing, and optionally or as necessary the        fluid supply tube; and    -   d) means for bleeding the flowpath,        such that fluid may be supplied to fill the flowpath tram the        fluid reservoir via the fluid supply tube (optionally or as        necessary via the means for flow switching) and recirculated by        the device through the flow path.

Where any pipe is described in connection with the operation of theapparatus as being connected or for connection to a (mating end of a)tube, e.g. a fluid supply tube, fluid recirculation tube or fluidofftake tube, the pipe and the tube may form a single integer in theflow path through which the circulating fluid from the wound passes.

In all embodiments of the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds, asignificant advantage, in particular in chronic wounds, is hat in usegranulation tissue is encouraged to grow onto and/or into the scaffoldthat lies between the wound film dressing and the wound bed.

The effect may be further enhanced by the circulation over the wound bedof irrigant from the fluid reservoir which contains nutrients for woundcells to aid proliferation, and other molecules that are beneficiallyinvolved in wound healing and/or that are favourable to the woundhealing process.

A further particular advantage is that it is unnecessary to remove thisgranulation tissue in-growth on dressing change, as the scaffold is leftbetween the wound film dressing and the wound bed to biodegrade. Thisminimises trauma and any need for debridement.

A more specific advantage is that the scaffold prevents the overgrowthof tissue in the wound area.

A particular advantage of this apparatus is its use with pressure sores:the device can be placed in the depths of the wound and the patient canlie upon it without either affecting the utility of the device orfurther damaging the wound. This becomes critical if the patient cannotbe moved from this posture for other medical reasons.

The scaffold is placed over substantially the expanse of the wound, andits size and configuration can be adjusted to •fit the individual wound.It can be formed from a variety of apertured, semi-rigid materials.

By ‘apertured’ herein is meant materials that are porous, apertured,holed, open-mesh, slit, incised and/or cut.

The material must be sufficiently apertured to allow for invasion by allmanner of cells involved in the process of tissue repair and woundhealing, and/or for the inward growth of blood vessels, and sufficientlyrigid to prevent wound overgrowth and collapse under suction.

Suitable biomaterials for the biodegradable scaffold includepoly(hydroxy acids) and esters thereof, such as poly(glycolic acid),poly(L-lactic acid), poly(D-lactic acid) and esters thereof, andcopolymers and blends of the aforementioned.

Suitable biomaterials also include poly(acid anhydrides), such aspoly(terephthalic acid), poly(adipic acid) and copolymers and blends ofthe aforementioned.

Additionally, biologically sourced biodegradable polymeric materials maybe used, such as substantially protein based polymers, for examplecollagens, fibronectins, or fibrins, either as whole molecules or thosesubjected to proteolytic or chemical treatments, in either degraded ornative conformations, or modified protein based polymers produced bynucleic acids recombinant techniques, for example, collagens,fibronectins, or fibrins, or fragments thereof, produced throughrecombinant DNA techniques; or blends thereof.

Further acceptable scaffolds will be combinations of protein-basedscaffolds and carbohydrate based polymers such as glycosoaminoglycans,chitosans, cellulose or alginate molecules.

Suitable materials also include human or animal derived tissuesprocessed in means to make them acceptable in placement into the woundsuch as skin, alimentary tract or connective tissues.

The scaffold may be formed in a variety of apertured, semi-rigid forms.

These forms may be essentially two-dimensional, such as sheets, layers,films, flexible panels, meshes, nets, webs or lattices. They may beplaced in the wound as dry, hydrated or gel based formulations.

One embodiment of apertured or holed scaffold comprises a section ofhoneycombed polymer sheet cut to the shape of the wound.

Where the scaffold is in an essentially two-dimensional apertured,semi-rigid form, such as a sheet, layer, film, flexible panel, mesh,net, web or lattice, it may be designed in a configuration that is ableto conform well to the wound bed on insertion into the wound.

This conforming to shape is then a particular advantage in thoseembodiments where the wound dressing is used on deeper wounds,especially where a wound filler is used to urge the wound dressingtowards the scaffold and wound bed, as described hereinafter inconnection with the wound dressing.

By way of example, such a scaffold may be in the form of a deeplyindented circular disc much like a multiple Maltese cross or a stylisedrose, as is described hereinafter in connection with an inlet manifoldshown in FIG. 18 b. This form is able to conform well to the wound bedon insertion into the wound, especially a deeper wound, by the armsclosing in and possibly overlapping.

The form of the scaffold may also be three-dimensional, such as sheets,layers, films, flexible panels, meshes, nets, webs and lattices, folded,creased, pleated, tucked, crinkled, crumpled, screwed up or twisted intoa three-dimensional form.

Alternatively, these forms may be inherently three-dimensional, such asmultilayers of films, flexible panels, meshes, nets, webs and lattices,or three-dimensional meshes, nets, webs and lattices, and favourablyfoams. They may be placed in the wound as dry, hydrated or gel basedformulations.

One embodiment of an apertured or holed scaffold comprises a section ofbiodegradable polymer mesh, which permits fluid supply towards the woundbed, the withdrawal of tissue fluid through the pores of the scaffoldand the ingrowth of cells to yield the eventual replacement of thescaffold with new tissue under the influence of the suction force.

A favoured embodiment of this apparatus comprises a section of knittedtwo- or three-dimensional mesh, in particular three-dimensional mesh. Apreferred embodiment of this apparatus comprises a section ofthree-dimensional mesh, sponge or felt as the biodegradable scaffold.

Such scaffold can vary in thickness and rigidity, although it ispreferred that a soft material be used for the patient's comfort if thepatient must lie upon the device during its operation.

Where the biodegradable scaffold comprises a mesh, the latter may beunwoven, woven or knitted, preferably knitted, and preferablythree-dimensional.

In all embodiments of the apparatus of this first aspect of-the presentinvention for aspirating, irrigating and/or cleansing wounds, aparticular advantage is the tendency of the wound dressing to conform tothe shape of the bodily part to which it is applied.

The wound dressing comprises a backing layer with a wound-facing facewhich is capable of forming a relatively fluid-tight seal or closureover a wound and at least one inlet pipe for connection to a fluidsupply tube or recirculation tube, which passes through and/or under thewound-facing face, and at least one outlet pipe for connection to afluid offtake tube, which passes through and/or under the wound-facingface, the point at which the or each inlet pipe and the or each outletpipe passes through and/or under the wound-facing face forming arelatively fluid-tight seal or closure.

The term “relatively fluid-tight seal or closure” is used herein toindicate one which is fluid- and microbe-impermeable and permits apositive or negative pressure of up to 50% atm., more usually up to 15%atm. to be applied to the wound. The term ‘fluid’ is used herein toinclude gels, e.g. thick exudate, liquids, e.g. water, and gases, suchas air, nitrogen, etc.

The shape of the backing layer that is applied may be any that isappropriate to aspirating, irrigating and/or cleansing the wound acrossthe area of the wound.

Examples of such include a substantially flat film, sheet or membrane,or a bag, chamber, pouch or other structure of the backing layer, e.g.of polymer film, which can contain the fluid.

The backing layer may be a film, sheet or membrane, often with a(generally uniform) thickness of up to 100 micron, preferably up to 50micron, more preferably up to 25 micron, and of 10 micron minimumthickness.

Its largest cross-dimension may be up to 500 mm (for example for largetorso wounds), up to 100 mm (for example for axillary and inguinalwounds), and up to 200 mm for limb wounds (for example for chronicwounds, such as venous leg ulcers and diabetic foot ulcers.

Desirably the dressing is resiliently deformable, since this may resultin increased patient comfort, and lessen the risk of inflammation of awound.

Suitable materials for it include synthetic polymeric materials that donot absorb aqueous fluids, such as polyolefins, such as polyethylenee.g. high-density polyethylene, polypropylene, copolymers thereof, forexample with vinyl acetate and polyvinyl alcohol, and mixtures thereof;polysiloxanes; polyesters, such as polycarbonates; polyamides, e.g. 6-6and 6-10, and hydrophobic polyurethanes.

They may be hydrophilic, and thus also include hydrophilicpolyurethanes.

They also include thermoplastic elastomers and elastomer blends, forexample copolymers, such as ethyl vinyl acetate, optionally or asnecessary blended with high-impact polystyrene.

They further include elastomeric polyurethane, particularly polyurethaneformed by solution casting.

Preferred materials for the present wound dressing include thermoplasticelastomers and curable systems.

The backing layer is capable of forming a relatively fluid-tight seal orclosure over the wound and/or around the inlet and outlet pipe(s).

However, in particular around the periphery of the wound dressing,outside the relatively fluid-tight seal, it is preferably of a materialthat has a high moisture vapour permeability, to prevent maceration ofthe skin around the wound. It may also be a switchable material that hasa higher moisture vapour permeability when in contact with liquids, e.g.water, blood or wound, exudate. This may, e.g. be a material that isused in Smith & Nephew's Allevyn™, IV3000™ and OpSite™ dressings.

The periphery of the wound-facing face of the backing layer may bear anadhesive film, for example, to attach it to the skin around the wound.

This may, e.g. be a pressure-sensitive adhesive, if that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound-facing face of the wound dressing.

Alternatively or additionally, where appropriate a light switchableadhesive could be used to secure the dressing in place to preventleakage. (A light switchable adhesive is one the adhesion of which isreduced by photocuring. Its use can be beneficial in reducing the traumaof removal of the dressing.)

Thus, the backing layer may have a flange or lip extending around theproximal face of the backing layer, of a transparent or translucentmaterial (for which it will be understood that materials that are listedabove are amongst those that are suitable).

This bears a film of a light switchable adhesive to secure the dressingin place to prevent leakage on its proximal face, and a layer of opaquematerial on its distal face.

To remove the dressing and not cause excessive trauma in removal of thedressing, the layer of opaque material on the distal face of the flangeor lip extending around the proximal wound is removed prior toapplication of radiation of an appropriate wavelength to the flange orlip.

If the periphery of the wound dressing, outside the relativelyfluid-tight seal, that bears an adhesive film to attach it to the skinaround the wound, is of a material that has a high moisture vapourpermeability or is a switchable material, then the adhesive film, ifcontinuous, should also have a high or switchable moisture vapourpermeability, e.g. be an adhesive such as used in Smith & Nephew'sAllevyn™, IV3000™ and OpSite™ dressings.

Where a vacuum, is applied to hold the wound dressing in place in afluid-tight seal around the periphery of the wound-facing face of thewound dressing, the wound dressing may be provided with a siliconeflange or lip to seal the dressing around the wound. This removes theneed for adhesives and associated trauma to the patient's skin.

Where the interior of, and the flow of irrigant and/or wound exudate toand through, the dressing is under any significant positive pressure,which will tend to act at peripheral points to lift and remove thedressing off the skin around the wound.

In such use of the apparatus, it may thus be necessary to provide meansfor forming and maintaining such a seal or closure over the woundagainst such positive pressure on the wound, to act at peripheral pointsfor this purpose.

Examples of such means include light switchable adhesives, as above, tosecure the dressing in place to prevent leakage.

Since the adhesion of a light switchable adhesive is reduced byphotocuring, thereby reducing the trauma of removal of the dressing, afilm of a more aggressive adhesive may be used, e.g. on a flange, asabove.

Examples of suitable fluid adhesives for use in more extreme conditionswhere trauma to the patient's skin is tolerable include ones thatconsist essentially of cyanoacrylate and like tissue adhesives, appliedaround the edges of the wound and/or the proximal face of the backinglayer of the wound dressing, e.g. on a flange or lip.

Further suitable examples of such means include adhesive (e.g. withpressure-sensitive adhesive) and non-adhesive, and elastic andnon-elastic straps, bands, loops, strips, ties, bandages, e.g.compression bandages, sheets, covers, sleeves, jackets, sheathes, wraps,stockings and hose, e.g. elastic tubular hose or elastic tubularstockings that are a compressive fit over a limb wound to apply suitablepressure to it when the therapy is applied in this way; and inflatablecuffs, sleeves, jackets, trousers, sheathes, wraps, stockings and hosethat are a compressive fit over a limb wound to apply suitable pressureto it when the therapy is applied in this way.

Such means may each be laid out over the wound dressing to extend beyondthe periphery of the backing layer of the wound dressing, and asappropriate will be adhered or otherwise secured to the skin around thewound and/or itself and as appropriate will apply compression (e.g. withelastic bandages, stockings) to a degree that is sufficient to hold thewound dressing in place in a fluid-tight seal around the periphery ofthe wound,

Such means may each be integral with the other components of thedressing, in particular the backing layer.

Alternatively, it may be permanently attached or releasably attached tothe dressing, in particular the backing layer, with an adhesive film,for example, or these components may be a Velcro™, push snap ortwist-lock fit with each other.

The means and the dressing may be separate structures, permanentlyunattached to each other.

In a more suitable layout for higher positive pressures on the wound, astiff flange or lip extends around the periphery of the proximal face ofthe backing layer of the wound dressing as hereinbefore defined.

The flange or lip is concave on its proximal face to define a peripheralchannel or conduit.

It has a suction outlet that passes through the flange or lip tocommunicate with the channel or conduit and may be connected to a devicefor applying a vacuum, such as a pump or a piped supply of vacuum.

The backing layer may be integral with or attached, for example byheat-sealing, to the flange or lip extending around its proximal face.

To form the relatively fluid-tight seal or closure over a wound that isneeded and to prevent passage of irrigant and/or exudate under theperiphery of the wound-facing face of the wound dressing, in use of theapparatus, the dressing is set on the skin around the wound.

The device then applies a vacuum to the interior of the flange or lip,thus forming and maintaining a seal or closure acting at peripheralpoints around the wound against the positive pressure on the wound.

With all the foregoing means of attachment, and means for forming andmaintaining a seal or closure over the wound, against positive ornegative pressure on the wound at peripheral points around the wound,the wound dressing sealing periphery is preferably of a generally roundshape, such as an ellipse, and in particular circular.

To form the relatively fluid-tight seal or closure over a wound andaround the inlet pipe(s) and outlet pipe(s) at the point at which theypass through and/or under the wound-facing face, the backing layer maybe integral with these other components.

The components may alternatively just be a push, snap or twist-lock fit:with each other, or adhered or heat-sealed together.

The or each inlet pipe or outlet pipe may be in the form of an aperture,such as a funnel, hole, opening, orifice, luer, slot or port forconnection as a female member respectively to a mating end of a fluidrecirculation tube and/or fluid supply tube (optionally or as necessaryvia means for forming a tube, pipe or hose, or nozzle, hole, opening,orifice, luer, slot or port for connection as a male member respectivelyto a mating end of a fluid recirculation tube and/or fluid supply tube(optionally or as necessary via means for flow switching between supplyand recirculation) or a fluid offtake tube.

Where the components are integral they will usually be made of the samematerial (for which it will be understood that materials that are listedabove are amongst those that are suitable).

Where, alternatively, they are a push, snap or twist-lock fit, the maybe of the same material or of different materials. In either case,materials that are listed above are amongst those that are suitable forall the components.

The or each pipe will generally pass through, rather than under thebacking layer. In such case, the backing layer may often have a rigidand/or resiliently inflexible or stiff area to resist any substantialplay between the or each pipe and the or each mating tube, ordeformation under pressure in any direction.

It may often be stiffened, reinforced or otherwise strengthened by aboss projecting distally (outwardly from the wound) around each relevanttube, pipe or hose, or nozzle, hole, opening, orifice, luer, slot orport for connection to a mating end of a fluid recirculation tube and/orfluid supply tube or fluid offtake tube.

Alternatively or additionally, where appropriate the backing layer mayhave a stiff flange or lip extending around the proximal face of thebacking layer to stiffen, reinforce or otherwise strengthen the backinglayer.

The wound dressing may not comprise any integer under the backing layerin the wound in use, other than the scaffold mentioned herein.

However, this may not provide a system to distribute irrigant over asufficient functional surface area to irrigate the wound at a practicalrate.

To be suitable for use, in particular in chronic wound dialysis, withrelatively high concentrations of materials that are deleterious towound healing, it may be advantageous to provide a system where woundirrigant and/or wound exudate may be distributed more evenly, or pass ina more convoluted path under the dressing over the scaffold in contactwith and overlying the wound bed.

Accordingly, one form of the dressing is provided with a ‘tree’ form ofpipes, tubes or tubules that radiate from an inlet manifold to thescaffold to end in apertures and deliver the circulating fluid directlyto the scaffold via the apertures. Similarly, there is an outletmanifold from which tubules radiate and run to the scaffold to end inopenings and collect the fluid directly from the scaffold.

The pipes, etc. may radiate regularly or irregularly through the woundin use, respectively from the inlet or outlet manifold, althoughregularly may be preferred. A more suitable layout for deeper wounds isone in which the pipes, etc. radiate hemispherically and concentrically,to the scaffold.

For shallower wounds, examples of suitable forms of such layout of thepipes, etc. include ones in which the pipes, etc. radiate in a flattenedhemiellipsoid and concentrically, to the scaffold.

Other suitable forms of layout of the pipes, etc. include one which havepipes, tubes or tubules extending from the inlet pipe(s) and/or outletpipe(s) at the point at which they pass through and/or under thewound-facing face of the backing layer to run over the scaffold. Thesemay have a blind bore with perforations, apertures, holes, openings,orifices, slits or slots along the pipes, etc.

These pipes, etc. then effectively form an inlet pipe manifold thatdelivers the circulating fluid directly to the scaffold or outletmanifold that collects the fluid directly from the wound respectively.

It does so via the holes, openings, orifices, slits or slots in thetubes, pipes, tubules, etc. over most of the scaffold under the backinglayer.

It may be desirable that the tubes, pipes or tubules are resilientlyflexible, e.g. elastomeric, and preferably soft, structures with goodconformability in the wound and the interior of the wound dressing.

When the therapy is applied in this way, the layout of the tubes, pipes,tubules, etc. may depend on the depth and/or capacity of the wound.

Thus, for shallower wounds, examples of suitable forms of such layout ofthe tubes, pipes, tubules, etc. include ones that consist essentially ofone or more of the tubes, etc. in a spiral.

A more suitable layout for deeper wounds when the therapy is applied inthis way may be one which comprises one or more of the tubes, etc. in ahelix or spiral helix.

Other suitable layouts for shallower wounds include one which haveblind-bore, perforated inlet pipe or outlet pipe manifolds thatcirculate fluid in the wound when the dressing is in use.

One or both of these may be such a form, the other may be, e.g. one ormore straight blind-bore, perforated radial tubes, pipes or nozzles.

Another suitable layout is one in which an inlet pipe and/or outlet pipemanifold that delivers the circulating fluid directly to the scaffold orcollects the fluid directly from the wound respectively via inlet and/oroutlet tubes, pipes or tubules, and the inlet manifold and/or outletmanifold is formed by slots in layers permanently attached to each otherin a stack, and the inlet and/or outlet tubes, pipes or tubules areformed by apertures through layers permanently attached to each other ina stack. (In FIG. 10 a there is shown an exploded isometric view of sucha stack, which is non-limiting.)

As also mentioned herein, the backing layer that is applied may be anythat is appropriate to the present system of therapy and permits apositive or negative pressure of up to 50% atm., more usually up to 25%atm. to be applied to the wound.

It is thus often a microbe-impermeable film, sheet or membrane, which issubstantially flat, depending on any pressure differential on it, andoften with a (generally uniform) thickness similar to such films orsheets used in conventional wound dressings, i.e. up to 100 micron,preferably to 50 micron, more preferably up to 25 micron, and of 10micron minimum thickness.

The backing layer may often have a rigid and/or resiliently inflexibleor stiff area to resist any substantial play between other componentsthat are not mutually integral, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

Such a form of dressing would not be very conformable to the wound bed,and may effectively form a chamber, hollow or cavity defined by abacking layer and the scaffold under the backing layer.

It may be desirable that the interior of the wound dressing conform tothe wound bed, even for a wound in a highly exuding state. Accordingly,one form of the dressing is provided with a wound filler under thebacking layer. This is favourably a resiliently flexible, e.g.elastomeric, and preferably soft, structure with good conformability towound shape. It is urged by its own resilience against the backing layerto apply gentle pressure on the scaffold and thence to the wound bed.

The wound filler may be integral with the other components of thedressing, in particular the backing layer.

Alternatively, it may be permanently attached to them/it, with anadhesive film, for example, or by heat-sealing, e.g. to a flange or lipextending from the proximal face, so as not to disrupt the relativelyfluid-tight seal or closure over the wound that is needed.

Less usually, the wound filler is releasably attached to the backinglayer, with an adhesive film, for example, or these components may be apush, snap or twist-lock fit with each other.

The wound filler and the backing layer may be separate structures,permanently unattached to each other.

The wound filler may be or comprise a solid integer, favourably aresiliently flexible, e.g. elastomeric, and preferably soft, structurewith good conformability to wound shape. Examples of suitable forms ofsuch wound fillers are foams formed of a suitable material, e.g. aresilient thermoplastic. Preferred materials for the present wounddressing include reticulated filtration polyurethane foams with smallapertures or pores.

Alternatively or additionally, it may be in the form of, or comprise oneor more conformable hollow bodies defined by a film, sheet or membrane,such as a bag, chamber, pouch or other structure, filled with a fluid orsolid that urges it to the wound shape.

The film, sheet or membrane, often has a (generally uniform) thicknesssimilar to that of films or sheets used in conventional wound dressingbacking layers.

That is, up to 100 micron, preferably up to 50 micron, more preferablyup to 25 micron, and of 10 micron minimum thickness, and is oftenresiliently flexible, e.g. elastomeric, and preferably soft.

Such a filler is often integral with the other components of thedressing, in particular the backing layer, or permanently attached tothem/it, with an adhesive film, for example, or by heat-sealing, e.g. toa flange.

Examples of suitable fluids contained in the hollow body or bodiesdefined by a film, sheet or membrane include gases, such as air,nitrogen and argon, more usually air, at a small positive pressure aboveatmospheric; and liquids, such as water, saline.

Examples also include gels, such as silicone gels, e.g. CaviCare™ gel,or preferably cellulosic gels, for example hydrophilic cross-linkedcellulosic gels, such as Intrasite™ cross-linked materials. Examplesalso include aerosol foams, where the gaseous phase of the aerosolsystem is air or an inert gas, such as nitrogen or argon, more usuallyair, at a small positive pressure above atmospheric; and solidparticulates, such as plastics crumbs.

Of course, if the backing layer is a sufficiently conformable and/ore.g. an downwardly dished sheet, the backing layer may lie under thewound filler, rather than vice versa.

In this type of layout, in order for the wound filler to urge the wounddressing towards the scaffold and wound bed, it will usually have to befirmly adhered or otherwise releasably attached to the skin around thewound.

This is especially the case in those embodiments where the wound fillerand the backing layer are separate structures, permanently unattached toeach other.

In such a layout for deeper wounds when the therapy is applied in thisway, the means for such attachment may also form and maintain a seal orclosure over the wound.

Where the filler is over the backing layer, and the fluid inlet pipe(s)and outlet pipe(s) pass through the wound-facing face of the backinglayer, they may run through or around the wound filler over the backinglayer.

One form of the dressing is provided with a wound filler under thebacking layer that is or comprises a resiliently flexible, e.g.elastomeric, and preferably soft, hollow body defined by a film, sheetor membrane, such as a bag, chamber, pouch or other structure, withapertures, holes, openings, orifices, slits or slots, or tubes, pipes,tubules or nozzles. It communicates with at least one inlet or outletpipe through at least one aperture, hole, opening, orifice, slit orslot.

The fluid contained in the hollow body may then be the circulating fluidin the apparatus.

The hollow body or each of the hollow bodies then effectively forms aninlet pipe or outlet pipe manifold that delivers the circulating fluiddirectly to the scaffold or collects the fluid directly from the woundrespectively via the holes, openings, orifices, slits• or slots, or thetubes, pipes or hoses, etc. in the film, sheet or membrane.

When the therapy is applied in this way, the type of the filler may alsobe largely determined by the depth and/or capacity of the wound.

Thus, for shallower wounds, examples of suitable wound fillers as acomponent of a wound dressing include ones that consist essentially ofone or more conformable hollow bodies defining an inlet pipe and/oroutlet pipe manifold that delivers the circulating fluid directly to thescaffold or collects the fluid directly from the wound.

A more suitable wound filler for deeper wounds when the therapy isapplied in this way may be one which comprises one or more conformablehollow bodies defined by, for example a polymer film, sheet or membrane,that at least partly surround(s) a solid integer. This may provide asystem with better rigidity for convenient handling.

Unless the wound filler under the backing layer effectively forms aninlet pipe or outlet pipe manifold with a direct connection between theinlet pipe(s) and outlet pipe(s) at the point at which they pass throughand/or under the wound-facing face, in order for irrigation of thescaffold to occur, it is appropriate for one or more bores, channels,conduits, passages, pipes, tubes, tubules and/or spaces, etc. to runfrom the point at which the fluid inlet pipe(s) and outlet pipe(s) passthrough and/or under the wound-facing face of the backing layer throughor around the wound filler under the backing layer.

Less usually, the wound filler is an open-cell foam with pores that mayform such bores, channels, conduits, passages and/or spaces through thewound filler under the backing layer.

Where the filler is or comprises one or more conformable hollow bodiesdefined by, for example a polymer film, sheet or membrane, it may beprovided with means for admitting fluids to the scaffold under the wounddressing.

These may be in the form of pipes, tubes, tubules or nozzles runningfrom the point at which the fluid inlet pipe(s) and outlet pipe(s) passthrough and/or under the wound-facing face of the backing layer throughor around the wound filler under the backing layer.

All of the suitable layouts for shallower wounds that compriseblind-bore, perforated inlet pipe or outlet pipe manifolds thatcirculate fluid in the wound when the dressing is in use, that aredescribed hereinbefore, may be used under a wound filler under thebacking layer.

In brief, suitable layouts include ones where one or both manifolds areannular or toroidal (regular, e.g. elliptical or circular, orirregular), optionally with blind-bore, perforated radial tubes, pipesor nozzles, branching from the annulus or torus; and/or in a meandering,tortuous, winding, zigzag, serpentine or boustrophedic (i.e. in themanner of a ploughed furrow) pattern, or defined by slots in andapertures through layers attached to each other in a stack.

Returning to the apparatus flowpath, the means for flow switchingbetween supply and recirculation may take any form that enables thewound simultaneously to be

-   -   a) put into communication with the fluid reservoir but    -   b) closed to the fluid recirculation tube, and    -   c) vice versa.

Thus, if there is only one inlet pipe that passes through and/or underthe wound-facing face of the wound dressing, the fluid reservoir isconnected by the fluid supply tube to the flow path via means for flowswitching as desired the into a fluid recirculation tube or a fluidofftake tube.

In this case, the means for flow switching between supply andrecirculation may be a regulator, such as a T-valve. This is connectedin turn to two parts of a fluid recirculation tube or a fluid offtaketube and the fluid supply tube, such that the desired flow switchingbetween supply and recirculation is achieved.

If there are two or more inlet pipes, these may be connectedrespectively to a fluid supply tube or fluid recirculation tube,respectively having a first regulator and a second regulator, such as avalve or other control device for admitting fluids into the wound.

The desired flow switching between supply and recirculation is achievedby respectively having the first regulator open when the secondregulator is shut, and vice versa.

The means for bleeding the flowpath may be situated in any appropriatepart of the apparatus that is in contact with the irrigant and/or woundexudate, but is usually within the offtake and/or recirculation tubes.However, it is often as far downstream of and away from the reservoirand the fluid supply tube as possible, so that it may be used to primethe whole of the flowpath from the fluid reservoir via the fluid supplytube.

It may be a regulator, such as a valve or other control device, e.g. aT-valve that is turned to switch between bleed and recirculation, forbleeding fluids from the apparatus, e.g. to a waste reservoir, such as acollection bag.

Alternatively, flow switching between supply and recirculation may notbe desired, but rather concomitant bleeding and/or recirculation isdesired.

The latter may occur when the volume of irrigant and/or wound exudate inrecirculation is increased by continuing addition to it of

-   -   a) wound exudate, and/or    -   b) fluid passing from a cleansing fluid through a selectively        permeable integer, for example in a system such as a dialysis        unit.

The means for bleeding the offtake and/or recirculation tubes may thenbe provided in the form of a regulator, such as a simple valve or othercontrol device for admitting or blocking the passage of irrigant and/orexudate through a bleed line branching from the recirculation path.

The means for fluid cleansing may as desired be a ‘single-phase system’.

In this, the circulating fluid from the wound and the fluid reservoirpasses through a self-contained system in which materials deleterious towound healing are removed and the cleansed fluid, still containingmaterials that are beneficial in promoting wound healing, is returnedvia the recirculation tube to the scaffold and the wound bed. Suchsystems are described in further detail hereinafter in connection withthe means for fluid cleansing.

Alternatively, where appropriate it may be provided in the form of atwo-phase system, such as a dialysis unit, or a biphasic liquidextraction unit.

In this, the circulating fluid from the wound and the fluid reservoirpasses through a system in which the fluid recirculates in indirect or(less usually, direct) contact with a second fluid (dialysate) phase,more usually a liquid, in which materials deleterious to wound healingare removed and the cleansed fluid, still containing materials that arebeneficial in promoting wound healing, is returned via the recirculationtube to the scaffold and the wound bed. Such systems are described infurther detail hereinafter in connection with the means for fluidcleansing.

In use, typically, the means for flow switching between supply andrecirculation tubes is set to admit fluid into the wound from the fluidreservoir but to close the wound to the fluid recirculation tube.

Then, any means for bleeding the offtake and/or recirculation tubes areis opened and the device for moving fluid through the wound and meansfor fluid cleansing is started.

The capacity of the apparatus flow path and the flow rate of irrigantand/or wound exudate from the wound will largely determine whether it isappropriate to run the device to prime the apparatus throughout thewhole length of the apparatus flow path, i.e. to displace any existingfluid reservoir (often air) from the fluid recirculation path, and forhow long it should be run. Typically, there is a preponderance ofirrigant from the fluid reservoir over wound exudate in recirculation,so that use of the device for moving fluid through the wound isappropriate for this purpose.

It is allowed to run until the apparatus is primed throughout the wholelength of the apparatus flow path.

Then, typically the means for bleeding the offtake and/or recirculationtubes is closed, and the means for flow switching between supply andrecirculation tubes is set to close the wound to the fluid reservoir butto admit fluid into the wound from the fluid recirculation tube.

If the means for fluid cleansing is a two-phase system, such as adialysis unit, or a biphasic extraction unit, the cleansing fluid istypically set in motion in contact with the surface of the selectivelypermeable integer, for example the polymer film, sheet or membrane. Ofcourse, the cleansing fluid may less usually be static, and then thisstep is omitted.

As noted below in more detail, the volume of irrigant and/or woundexudate from the wound in recirculation may be increased by continuingaddition to it of

-   -   a) wound exudate, and/or    -   b) fluid passing from a cleansing fluid through a selectively        permeable integer, for example the polymer film, sheet or        membrane• of a two-phase system, such as an dialysis unit.

Additionally or alternatively, it may be desired to apply a negativepressure to the wound by means of a device for moving fluid through thewound and means for fluid cleansing applied to the fluid inrecirculation in the fluid recirculation tube downstream of and awayfrom the wound dressing.

In such case, it may be desirable to provide a system in whichconcomitant bleeding and/or recirculation is possible, and to make thenecessary adjustments to maintain the desired balance of fluid inrecirculation by means of the means for bleeding the offtake and/orrecirculation tubes.

The volume of irrigant and/or wound exudate from the wound inrecirculation may be decreased by continuing loss from it of fluidpassing from a cleansing fluid through a selectively permeable integer,for example in a system such as a dialysis unit.

Additionally or alternatively, it may be desired to apply a positivepressure to the wound by means of a device for moving fluid through thewound and means for fluid cleansing applied to the fluid inrecirculation in the fluid recirculation tube upstream of and towardsthe wound dressing.

The means for flow switching between supply and recirculation may besimilarly provided in a form in which concomitant supply and/orrecirculation is possible, and to make the necessary adjustments tomaintain the desired balance of fluid in recirculation by means of themeans for flow switching.

It will be appreciated that where a positive or negative pressure is tobe applied to the wound, at least one hollow body in the recirculationflow path to and from the scaffold and the wound bed should havesufficient resilience against the pressure to allow any significantcompression or decompression of the irrigant fluid to occur.

In all embodiments of the apparatus, the type and material of suchbodies (which are defined by a film, sheet or membrane) that aredescribed by way of example herein to be suitable for use in the presentinvention will be largely capable of this function.

Thus, examples of suitable materials for bodies defined by a film, sheetor membrane include suitably elastically resilient thermoplasticmaterials that are potentially capable of this function when pressure isapplied in this way.

Such bodies include inlet or offtake and/or recirculation tubes andstructures such as bags, chambers and pouches, filled with irrigantfluid, e.g. under the backing layer of the wound dressing.

The present invention in this aspect provides several advantages.

One is that application of circulating irrigant fluid passing overand/or through the scaffold in contact with and overlying the wound bedmay be used to supply the tissue underlying the wound with one or morephysiologically active components.

This may be effected in therapeutically active amounts, to promotegreater wound healing than by treatment with the fluid physiologicallyactive component(s) alone.

Such physiologically active components of the exudate that arebeneficial to wound healing may be e.g. be enzymes, nutrients for woundcells to aid proliferation, and other molecules that are beneficiallyinvolved in wound healing, such as growth factors, enzymes and otherproteins and derivatives.

They may be supplied to any integer in the recirculation path in directcontact with the fluid, e.g. the reservoir or from the dialysate of adialytic means for fluid cleansing.

Circulating wound fluid aids in movement of

-   -   a) biological signalling molecules involved in wound healing to        locations in the wound bed that are favourable to the wound        healing process and/or to cells that would otherwise not be        exposed to them, e.g. in a highly exuding wound; and    -   b) nutrients for wound cells to aid proliferation, and other        molecules that are beneficially involved in wound healing.

This is especially the case in those embodiments of the apparatus ofthis first aspect of the present invention for aspirating, irrigatingand/or cleansing wounds where there is an inlet or outlet manifold thatdelivers or collects the fluid directly from the scaffold over anextended area.

Such materials include cytokines, enzymes, nutrients for wound cells toaid proliferation, oxygen, and other molecules that are beneficiallyinvolved in wound healing, such as growth factors, and others havingbeneficial effects (which may be further enhanced) in causingchemotaxis.

The inlet and/or outlet tubes, the fluid recirculation tube and thefluid supply tube, etc. may be of conventional type, e.g. of ellipticalor circular cross-section, and may suitably have a uniform cylindricalbore, channel, conduit or passage throughout their length.

Depending on the desired fluid volume flow rate of irrigant and/or woundexudate from the wound, and the desired amount in recirculation,suitably the largest cross-dimension of the bore may be up to 10 mm forlarge torso wounds, and up to 2 mm for limb wounds.

The tube walls should suitably thick enough to withstand any positive ornegative pressure on them, in particular if the volume of irrigantand/or wound exudate from the wound in recirculation is increased bycontinuing addition to it of wound exudate, and/or fluid passing from acleansing fluid through a selectively permeable integer, for example thepolymer film, sheet or membrane of a two-phase system, such as andialysis unit.

However, as noted below with regard to pumps, the prime purpose of suchtubes is to convey fluid irrigant and exudate through the length of theapparatus flow path, rather than to act as pressure vessels.

The tube walls may suitably be at least 25 micron thick.

The bore or any perforations, apertures, holes, openings, orifices,slits or slots along the pipes, etc. or in the hollow body or each ofthe hollow bodies may be of small cross-dimension.

They may then effectively form a macroscopic and/or microscopic filterfor particulates including cell debris and micro-organisms, whilstallowing proteins and nutrients to pass through.

Such tubes, pipes or hoses, etc. through and/or around the filler,whether the latter is a solid integer and/or one or more resilientlyflexible or conformable hollow bodies, are described in further detailhereinbefore in connection with the inlet pipe(s) and outlet pipe(s).

The whole length of the apparatus for aspirating, irrigating and/orcleansing wounds should be microbe-impermeable once the wound dressingis over the wound in use.

It is desirable that the wound dressing and the interior of theapparatus for aspirating, irrigating and/or cleansing wounds of thepresent invention is sterile.

The fluid may be sterilised in the fluid reservoir and/or the rest ofthe system in which the fluid recirculates, including the means forfluid cleansing, by ultraviolet, gamma or electron beam irradiation.

This way, in particular reduces or eliminates contact of internalsurfaces and the fluid with any sterilising agent.

Examples of other methods of sterilisation of the fluid also includee.g. the use of ultrafiltration through microapertures or micropores,e.g. of 0.22 to 0.45 micron maximum cross-dimension, to be selectivelyimpermeable to microbes; and fluid antiseptics, such as solutions ofchemicals, such as chlorhexidine and povidone iodine; metal ion sources,such as silver salts, e.g. silver nitrate; and hydrogen peroxide;although the latter involve contact of internal surfaces and the fluidwith the sterilising agent.

It may be desirable that the interior of the wound dressing, the rest ofthe system in which the fluid recirculates, and/or the scaffold and thewound bed. even for a wound in a highly exuding state, are kept sterileafter the fluid is sterilised in the fluid reservoir, or that at leastnaturally occurring microbial growth is inhibited.

Thus, materials that are potentially or actually beneficial in thisrespect may be added to the irrigant initially, and as desired theamount in recirculation increased by continuing addition.

Examples of such materials include antibacterial agents (some of whichare listed above), and antifungal agents.

Amongst those that are suitable are, for example triclosan, iodine,metronidazole, cetrimide, chlorhexidine acetate, sodium undecylenate,chlorhexidine and iodine.

Buffering agents, such as potassium dihydrogen phosphate/disodiumhydrogen phosphate. may be added to adjust the pH, as may localanalgesics/anaesthetics, such as lidocaine/lignocaine hydrochloride,xylocaine (adrenaline, lidocaine) and/or anti-inflammatories, to reducewound pain or inflammation or pain associated with the dressing.

It is also desirable to provide a system in which physiologically activecomponents of the exudate that are beneficial to wound healing are notremoved before or after the application of fluid cleansing, e.g. by thepassive deposition of materials that are beneficial in promoting woundhealing, such as proteins, e.g. growth factors.

This may occur at any point at least one inlet or outlet pipe through atleast one aperture, hole, opening, orifice, slit or slot.

The fluid contained in the hollow body may aid deposition of materialsthat are beneficial in promoting wound healing, and consequent coating,

-   -   a) may be added to the irrigant initially, and as desired the        amount in recirculation increased by continuing addition, or    -   b) may be used at any point or on any integer in the        recirculation path in direct contact with the fluid, e.g. on the        means for fluid cleansing or any desired tube or pipe.

Examples of coating materials for surfaces over which the circulatingfluid passes include anticoagulants, such as heparin, and high surfacetension materials, such as PTFE, and polyamides, which are useful forgrowth factors, enzymes and other proteins and derivatives.

The apparatus of the invention for aspirating, irrigating. and/orcleansing wounds is provided with means for admitting fluids directly orindirectly to the wound under the wound dressing in the form of a fluidsupply tube to a fluid reservoir.

The fluid reservoir may be of any conventional type, e.g. a tube, bag(such as a bag typically used for blood or blood products, e.g. plasma,or for infusion feeds, e.g. of nutrients), chamber, pouch or otherstructure, e.g. of polymer film, which can contain the irrigant fluid.

The reservoir may be made of a film, sheet or membrane, often with a(generally uniform) thickness similar to that of films or sheets used inconventional wound dressing backing layers, i.e. up to 100 micron,preferably up to 50 micron, more preferably up to 25 micron, and of 10micron minimum thickness, and is often a resiliently flexible, e.g.elastomeric, and preferably soft, hollow body.

In all embodiments of the apparatus the type and material of the tubesthroughout the apparatus of the invention for aspirating, irrigatingand/or cleansing wounds and the fluid reservoir will be largelydetermined by their function.

To be suitable for use, in particular on chronic timescales, thematerial should be non-toxic and biocompatible, inert to any activecomponents, as appropriate of the irrigant from the fluid reservoirand/or wound exudate in the apparatus flow path, and, in any use of atwo-phase system dialysis unit, of the dialysate that moves into thecirculating fluid in the apparatus.

When in contact with irrigant fluid, it should not allow any significantamounts of extractables to diffuse freely out of it in use of theapparatus.

It should be sterilisable by ultraviolet, gamma or electron beamirradiation and/or with fluid antiseptics, such as solutions ofchemicals, fluid- and microbe-impermeable once in use, and flexible.

Examples of suitable materials for the fluid reservoir include syntheticpolymeric materials, such as polyolefins, such as polyethylene, e.g.high-density polyethylene and polypropylene.

Suitable materials for the present purpose also include copolymersthereof, for example with vinyl acetate and mixtures thereof. Suitablematerials for the present purpose further include medical gradepoly(vinyl chloride).

Notwithstanding such polymeric materials, the fluid reservoir will oftenhave a stiff area to resist any substantial play between it andcomponents that are not mutually integral, such as the fluid supply tubetowards the wound dressing, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

The device for moving fluid through the wound and means for fluidcleansing may be any appropriate for this purpose, and may act at anyappropriate point for this purpose.

It may apply a positive or negative pressure to the wound, although itsprime purpose is to move fluid (irrigant from the fluid reservoir and/orwound exudate through the length of the apparatus flow path, rather thanto apply a positive or negative pressure to the wound.

If applied to the fluid in recirculation in the fluid recirculation tubeupstream of and. towards the wound dressing and/or the fluid in thefluid supply tube towards the wound dressing (optionally or as necessaryvia means for flow switching between supply and recirculation), it willusually apply positive pressure (i.e. above-atmospheric pressure) to thewound bed.

Often the means for fluid cleansing is (most appropriately for itspurpose) downstream of the wound dressing, and provides the highestresistance in the flow path.

This is especially the case where the means for fluid cleansing is asingle-phase system, e.g. with ultrafiltration through microapertures ormicropores, thus enhancing applied positive pressure to the wound.

Where the device is applied to the fluid in recirculation in the fluid•recirculation tube and/or the fluid in the fluid offtake tube downstreamof and away from the wound dressing, it will usually apply negativepressure (i.e. below-atmospheric pressure or vacuum) to the wound bed.

Again, often the means for fluid cleansing is (most appropriately forits purpose) downstream of the wound dressing, and provides the highestresistance in the flow path, thus enhancing applied negative pressure tothe wound.

The following types of pump may be used as desired: reciprocating pumps,such as:

-   -   shuttle pumps—with an oscillating shuttle mechanism to move        fluids at rates from 2 to 50 ml per minute;    -   diaphragm pumps—where pulsations of one or two flexible        diaphragms displace liquid while check valves control the        direction of the fluid flow.    -   piston pumps—where pistons pump fluids through check valves, in        particular for positive and/or negative pressure on the wound        bed.    -   rotary pumps, such as: centrifugal pumps flexible impeller        pumps—where elastomeric impeller traps fluid between impeller        blades and a moulded housing that sweeps fluid through the pump        housing.    -   progressing cavity pumps—with a cooperating screw rotor and        stator, in particular for higher-viscosity and        particulate-filled exudate;    -   rotary vane pumps—with rotating vaned disk attached to a drive        shaft moving fluid without pulsation as it spins. The outlet can        be restricted without damaging the pump.    -   peristaltic pumps—with peripheral rollers on rotor arms acting        on a flexible fluid circulation tube to urge fluid current flow        in the tube in the direction of the rotor.

The type and/or capacity of the device will be largely determined by

-   -   a) the appropriate or desired fluid volume flow rate of irrigant        and/or wound exudate from the wound, and    -   b) whether it is appropriate or desired to apply a positive or        negative pressure to the wound bed and the level of such        pressure to the wound bed.    -   for optimum performance of the wound healing process, and by        factors such as portability, power consumption and isolation        from contamination.

Such a device may also suitably be one that is capable of pulsed,continuous, variable, reversible and/or automated and/or programmablefluid movement. It may in particular be a pump of any of these types.

In practice, even from a wound in a highly exuding state, such a rate ofexudate flow is only of the order of up to 75 microlitres/cm²/hr (wherecm² refers to the wound area), and the fluid can be highly mobile (owingto the proteases present).

Exudate levels drop and consistency changes as the wound heals, e.g. toa level for the same wound that equates to 12.5-25 microlitres/cm²/hr.

Where materials deleterious to wound healing are removed by a two-phasesystem (see below.}, such as a dialysis unit, fluid is also potentiallylost to the system through the means for fluid cleansing.

This may occur, e.g. through a dialysis polymer film, sheet or membranewhich is also permeable to water, in addition to materials deleteriousto wound healing.

The balance of fluid in recirculation may thus further decrease, but maybe adjusted to minimise this undesired loss in a routine manner asdescribed hereinbefore.

Hence, it will be seen that the circulating fluid from the wound willtypically contain a preponderance of irrigant over wound exudate inrecirculation from the fluid reservoir.

The type and/or capacity of the device will thus be largely determinedin this respect by the appropriate or desired fluid volume flow rate ofirrigant, rather than that of exudate, from the wound.

In practice, such a rate of flow of total irrigant and/or wound. exudatewill be of the order of 1 to 1000, e.g. 3 to 300, and less preferably 1to 10 ml/cm²/24 hour, where the cm² refers to the wound area.

The volume of irrigant and/or wound exudate in recirculation may varyover a wide range, but will typically be e.g. 1 to 8 I. (for example forlarge torso wounds), 200 to 1500 ml (for example for axillary andinguinal wounds), and 0.3 to 300 ml for limb wounds when the therapy isapplied in this way.

In practice, suitable pressures are of the order of up to 25% atm suchas up to 10% atm. positive or negative pressure on the wound bed, theapparatus being operated as a closed recirculating system.

The higher end of these ranges are potentially more suitable forhospital use, where relatively high % pressures and/or vacua may be usedsafely under professional supervision.

The lower end is potentially more suitable for home use, whererelatively high % pressures and/or vacua cannot be used safely withoutprofessional supervision, or for field hospital use.

The device may be a peristaltic pump or diaphragm pump, e.g. preferablya small portable diaphragm or peristaltic pump.

These are preferred types of pump, in order in particular to reduce oreliminate contact of internal surfaces and moving parts of the pump with(chronic) wound exudate, and for ease of cleaning.

It may suitably be one that applies positive pressure to the woundand/or the means for fluid cleansing. A preferred pump when. the appliedpressure is positive is a peristaltic pump, e.g. a small, portableperistaltic pump, •mounted upstream of the means for fluid cleansing.

Where the pump is a peristaltic pump, this may be e.g. an Instech ModelP720 miniature peristaltic pump, with a flow rate: of 0.2-180 ml/hr anda weight of <0.5 k. This is potentially useful for home and fieldhospital use.

Where the pump is a peristaltic pump, this may be e.g. an Instech ModelP720 miniature peristaltic pump, with a flow rate: of 0.2-180 ml/hr anda weight of <0.5 k. This is potentially useful for home and fieldhospital use.

The pump may suitably be one that applies negative pressure to the woundand/or the means for fluid cleansing. A preferred pump when the appliedpressure is negative is a diaphragm pump, e.g. a small, portablediaphragm pump, mounted downstream of the dressing or the means forfluid cleansing.

Where the pump is a diaphragm pump, and preferably a small portablediaphragm pump, the one or two flexible diaphragms that displace liquidmay each be, for example a polymer film, sheet or membrane, that isconnected to means for creating the pulsations. This may be provided inany form that is convenient, inter alia as a piezoelectric transducer, acore of a solenoid or a ferromagnetic integer and coil in which thedirection of current flow alternates, a rotary cam and follower, and soon.

The outlet from the dressing passes to the means for fluid cleansing forremoval of materials deleterious to wound healing from wound exudate,and in turn to the fluid recirculation tube(s).

The apparatus of the invention for aspirating, irrigating and/orcleansing wounds is provided with means for fluid cleansing, which maybe

-   -   a) a single-phase system, such as an ultrafiltration unit, or a        chemical absorption and/or adsorption unit; or    -   b) a two-phase system, such as a dialysis unit, or a biphasic        extraction unit.

In the former, circulating fluid from the wound and the fluid reservoirpasses through a self-contained system in which materials deleterious towound healing are removed and the cleansed fluid, still containingmaterials that are beneficial in promoting wound healing are returned tothe wound.

The single-phase system may be of any conventional type.

Examples of the means for fluid cleansing in such a system include amacro- or microfiltration unit, which appropriately comprises one ormore macroscopic and/or microscopic filters.

These are to retain particulates, e.g. cell debris and micro-organisms,allowing proteins and nutrients to pass through.

Alternatively, they also include an ultrafiltration unit, such as a onein which the cleansing integer is a filter for materials deleterious towound healing, for example a high throughput, low protein-bindingpolymer film, sheet or membrane which is selectively impermeable tomaterials deleterious to wound healing, which are removed and thecleansed fluid, still containing materials that are beneficial inpromoting wound healing is passed by it.

The membrane may preferably be of a hydrophilic polymeric material, suchas a cellulose acetate-nitrate mixture, polyvinylidene chloride, and,for example hydrophilic polyurethane.

Examples of less preferred materials include hydrophobic materials alsoincluding polyesters, such as polycarbonates, PTFE, and polyamides, e.g.6-6 and 6.-10, and hydrophobic polyurethanes, and quartz and glassfibre.

It has microapertures or micropores, the maximum cross-dimension ofwhich will largely depend on the species that are to be selectivelyremoved in this way and those to which it is to be permeable.

The former may be removed with microapertures or micropores, e.g.typically with a maximum cross-dimension in the range of 20 to 700micron, g. 20 to 50 nm (for example for undesired proteins), 50 to 100nm, 100 to 250 nm, 250 to 500 nm and 500 to 700 nm.

The filter integer may be a flat sheet or a membrane of a polymericmaterial in a more convoluted form, e.g. in the form of elongatestructure, such as pipes, tubules, etc.

The system may be a chemical adsorption unit, for example one in which aparticulate, such as a zeolite, or a layer, e.g. of a functionalisedpolymer has sites on its surface that are capable of removing materialsdeleterious to wound healing on passing the circulating fluid from thewound and the fluid reservoir over them.

The materials may be removed, e.g. by destroying or binding thematerials that are deleterious to wound healing, by, for examplechelators and/or ion exchangers, degraders, which may be enzymes.

Examples of such also include less specific chemical absorption and/oradsorption units, for example one in which a physical absorbent, such asactivated carbon or a zeolite, has non-specific sites on its surfacethat are capable of removing materials deleterious to wound healing onpassing the circulating fluid from the wound and the fluid reservoirover them.

The cleansing integer, for example the polymer film, sheet or otherchemical absorption and/or adsorption means, etc. should of course becapable of removing materials deleterious to wound healing at apractical rate for a given capacity of the apparatus flow path and theflow rate of irrigant.

In the two-phase system, circulating fluid from the wound and the fluidreservoir in indirect or (less usually, direct) contact with a secondfluid (dialysate) phase, more usually a liquid.

Thus, in one form, a biphasic liquid extraction unit, the second fluidphase is (usually) a liquid that is immiscible with the circulatingfluid from the dressing, over a surface of which the circulating fluidpasses in direct contact with the cleansing fluid. Materials deleteriousto wound healing are removed into the dialysate, and the cleansed fluid,still containing materials that are beneficial in promoting woundhealing, is returned via the recirculation tube to the wound bed.

Examples of such means for fluid cleansing include those wherein thesecond fluid (dialysate) phase is perfluorodecalin and like materials

Alternatively, where appropriate it may be provided in a form in whichthe two fluids (recirculation fluid and dialysate) are separated by asignificantly two-dimensional integer, for example a polymer film, sheetor membrane or hollow fibre or filament that is permeable to materialsin the circulating fluid in the apparatus.

Again, materials deleterious to wound healing are removed into thedialysate, and the cleansed fluid, still containing materials that arebeneficial in promoting wound healing, is returned via the recirculationtube to the wound bed.

In either form in which the two-phase system, such as a dialysis unit,is provided, in use typically the dialysate moves past the circulatingfluid in the apparatus in a co- or preferably counter-current direction.

Pumps, such as peristaltic pumps, and/or valves control the direction ofthe two fluid flows.

However, the cleansing fluid may less usually be static, although thismay not provide a system with sufficient (dynamic) surface area toremove materials deleterious to wound healing from wound exudate at apractical rate.

Typical dialysate flow rates in a dialytic means for fluid cleansing inthe present apparatus for aspirating, irrigating and/or cleansing woundsare those used in the conventional type of two-phase system, such as adialysis unit for systemic therapy.

The integer may be a film, sheet or membrane, often of the same type,and of the same (generally uniform) thickness, as those used inconventional two-phase system, such as a dialysis unit for systemictherapy.

The film, sheet or membrane may be substantially flat, and depending onany pressure differential across it may require other materials on or init to stiffen, reinforce or otherwise strengthen it.

However, this may not provide a system with sufficient functionalsurface area to remove materials deleterious to wound healing from woundexudate at a practical rate.

The surface area of any such film, sheet or membrane may be suitably beno less than 50 mm², such 100 to 1000000 mm², e.g. 500 to 25000 mm².

To be suitable for use, in particular in chronic wound dialysis, withrelatively high concentrations of materials that are deleterious to’wound healing, it may be advantageous to provide a system in which thefilm, sheet or membrane of a polymeric material is in a more convolutedform.

This may be in the form of elongate structures, such as pipes, tubeshollow fibres or filaments or tubules of a round cross-section, e.g.elliptical or circular, e.g. in a parallel array with spacestherebetween.

The wound irrigant and/or wound exudate may recirculate through theinside and the cleansing fluid may pass into the spaces between adjacentpipes, tubes or tubules in a co- or preferably counter-currentdirection, or vice versa.

Again, materials deleterious to wound healing are removed into thedialysate, and the cleansed fluid, still containing materials that arebeneficial in promoting wound healing, is returned via the recirculationtube to the wound.

Where the means for fluid cleansing is a two-phase system, e.g. in theform of a dialysis unit, or a biphasic extraction unit, the circulatingfluid from the wound and the fluid reservoir passes across one surfacesof a significantly two-dimensional integer, for example a polymer film,sheet or membrane which is selectively permeable to materialsdeleterious to wound healing.

These are removed by passing a cleansing fluid across the other surfaceof the integer. The integer may be a film, sheet or membrane that isselectively permeable to the foregoing materials deleterious to woundhealing.

Examples of these as above include oxidants, such as free radicals, e.g.peroxide and superoxide; iron II and iron III;

all involved in oxidative stress on the wound bed;

basic or acidic species which adversely affect the pH in the woundexudate, such as protons.

proteases, such as serine proteases, e.g. elastase and thrombin;cysteine proteases; matrix metalloproteases, e.g. collagenase; andcarboxyl (acid) proteases;

endotoxins, such as lipopolysaccharides;

bacterial autoinducer signalling molecules, such as homoserine lactonederivatives, e.g. oxo-alkyl derivatives;

inhibitors of angiogenesis such as thrombospondin-1 (TSP-1), plasminogenactivator inhibitor, or angiostatin (plasminogen fragment);

pro-inflammatory cytokines such as tumour necrosis factor alpha (TNFα)and interleukin 1 beta (IL-1β); and

inflammatories, such as lipopolysaccharides, and e.g. histamine.

Examples of suitable materials for the film, sheet or membrane(typically in the form of conformable hollow bodies defined by the film,sheet or membrane, such as the structures described hereinbefore)include natural and synthetic polymeric materials.

The membrane may be of one or more hydrophilic polymeric materials, suchas a cellulose derivative, e.g. regenerated cellulose, a cellulosemono-, di- or tri-esters, such as cellulose mono-, di- or tri-acetate,benzyl cellulose and Hemophan, and mixtures thereof.

Examples of other materials include hydrophobic materials, such asaromatic polysulphones, polyethersulphones, polyetherether-sulphones,polyketones, polyetherketones and polyetherether-ketones, andsulphonated derivatives thereof, and mixtures thereof.

Examples of other materials include hydrophobic materials, such aspolyesters, such as polycarbonates and polyamides, e.g. 6-6 and 6-10;polyacrylates, including, e.g. poly(methyl methacrylate),polyacrylonitrile and copolymers thereof, for exampleacrylonitrile-sodium metallosulphonate copolymers; and poly(vinylidenechloride).

Suitable materials for the present membranes include thermoplasticpolyolefins, such as polyethylene e.g. high-density polyethylene,polypropylene, copolymers thereof, for example with vinyl acetate andpolyvinyl alcohol, and mixtures thereof.

The dialysis membrane should have a molecular weight cut off (MWCO)chosen to allow selective perfusion of species deleterious to woundhealing that have been targeted for removal from the wound. For example,perfusion of the serine protease elastase (molecular weight 25900Dalton) would require a membrane with MWCO >25900 Dalton. The MWCOthreshold can be varied to suit each application between 1 and 3000000Dalton.

Preferably, the MWCO should be as close as possible to this weight toexclude interference by larger competitor species.

For example, such a membrane with MWCO >25900 Dalton does not allow anysignificant amounts of the antagonist to elastase, alpha-1-antitrypsin(AAT) (molecular weight 54000 Dalton), which occurs naturally in wounds,to diffuse freely out of the wound fluid into the dialysate.

The inhibitor, which is beneficial in promoting chronic wound healing,remains in contact with the wound bed, and can act beneficially on it,whilst the elastase that is deleterious to wound healing is removed.

Such use of the present apparatus is, e.g. favourable to the woundhealing process in chronic wounds, such as diabetic foot ulcers, andespecially decubitus pressure ulcers.

As noted hereinafter, antagonists, for example degrading enzymes, orsequestrating agents for elastase on the dialysate side of the membrane,may be used to enhance the removal of this protease from wound exudate.

Where it is desired to remove several different materials that aredeleterious to wound healing, it may be advantageous to provide a systemof modules in series, each of which removes a different material. Thisallows incompatible cleansing materials to be used on the same fluidand/or wound exudates.

Preferably any such system is a conventional automated, programmablesystem which can cleanse the wound irrigant and/or wound exudate withminimal supervision.

As noted above in more detail, fluid passes from a cleansing fluidthrough a selectively permeable integer.

This may be the typical permeable polymer film, sheet or membrane of atwo-phase system, such as a dialysis unit.

Additionally, solutes or disperse phase species will pass from thedialysate into the irrigant and/or wound exudate through the dialysispolymer film, sheet or membrane.

This property may be used to perfuse materials beneficial to woundhealing into the irrigant and/or exudate from a dialysate.

In this less conventional type of infusion feed, a broad spectrum ofspecies will usually pass into the exudate and/or irrigant fluid fromthe dialysate.

These include ionic species, such as bicarbonate; vitamins, such asascorbic acid (vitamin C) and vitamin E, and stable derivatives thereof,and mixtures thereof; to relieve oxidative stress on the wound bed; pHbuffering agents, such as potassium dihydrogen phosphate/disodiumhydrogen phosphate, local analgesics/anesthetics, such aslidocaine/lignocaine hydrochloride and xylocaine (adrenaline lidocaine)and/or anti-inflammatories, to reduce wound pain or inflammation or painassociated with the dressing nutrients to aid proliferation of woundcells, such as amino acids, sugars, low molecular weight tissue buildingblocks and trace elements; and other cell culture medium species; andgases, such as air, nitrogen, oxygen and/or nitric oxide; and agents forthe adjustment of pH in the wound exudate, such as base or acidscavengers and/or ion exchangers, or other species, which may benon-labile, insoluble and/or immobilised) species, such as ScavengePore®phenethyl morpholine (Aldrich).

For the purposes of fluid cleansing in the apparatus of the presentinvention, both the single-phase system, such as an ultrafiltrationunit, and two-phase system, such as a dialysis unit, may have captive(non-labile, insoluble and/or immobilised) species such as thefollowing, bound to an insoluble and/or immobilised) substrate overand/or through which the irrigant and/or wound exudate from, the wounddressing passes in turn to the fluid recirculation tube(s): antioxidantsand free radical scavengers, such as 3-hydroxytyramine (dopamine),ascorbic acid (vitamin C), vitamin E and glutathione, and stablederivatives thereof, and mixtures thereof; to relieve oxidative stresson the wound bed; metal ion chelators and/or ion exchangers, such astransition metal ion chelators, such as iron Ill chelators (Fe Ill isinvolved in oxidative stress on the wound bed.), such as desferrioxamine(DFO), 3-hydroxytyramine (dopamine), chelators and/or ion exchanges,such as desferrioxamine (DFO), 3-hydroxytyramine (dopamine); agents forthe adjustment of pH in the wound exudate, such as base or acidscavengers and/or ion exchangers, or other species, which may benon-labile, insoluble and/or immobilised) species, such as ScavengePore®phenethyl morpholine (Aldrich); iron Ill reductants; proteaseinhibitors, such as TIMPs and alpha 1-antitrypsin (AAT); serine proteaseinhibitors, such as 4-(2-aminoethyl)-benzene sulphonyl fluoride (AEBSF,PefaBloc) and Nα-p-tosyl-L-lysine chloro-methyl ketone (TLCK) andε-aminocaproyl-p-chlorobenzylamide; cysteine protease inhibitors; matrixmetalloprotease inhibitors; and carboxyl (acid) protease inhibitors;sacrificial redox materials that are potentially or actually beneficialin promoting wound healing, by the removal of materials that trigger theexpression into wound exudate of redox-sensitive genes that aredeleterious to wound healing; autoinducer signalling molecule degraders,which may be enzymes; and anti-inflammatory materials to bind or destroylipopolysaccharides, e.g. peptidomimetics

Other physiologically active components of the exudate that aredeleterious to wound healing may be removed in this way.

These may be removed with suitable chelators and/or ion exchangers,degraders, which may be enzymes, or other species.

The following types of functionalised substrate has sites on its surfacethat are capable of removing materials deleterious to wound healing onpassing the circulating fluid from the wound and the fluid reservoirover them: heterogeneous resins, for example silica-supported reagentssuch as: metal scavengers, 3-(diethylenetriamino)propyl-functionalisedsilica gel 2-(4-(ethylenediamino)benzene)ethyl-functionialised silicagel 3-(mercapto)propyl-functionalised silica gel3-(1-thioureido)propyl-functionalised silica gel triaminetetraacetate-functionalised silica gel or electrophilic scavengers,4-carboxybutyl-functionalised silica gel 4-ethyl benzenesulfonylchloride-functionalised silica gel propionyl chloride-functionalisedsilica gel 3-(isocyano)propyl-functionalised silica gel3-(thiocyano)propyl-functionalised silica gel 3-(2-succinicanhydride)propyl-functionalised silica gel3-(maleimido)propyl-functionalised silica gel or nucleophilicscavengers, 3-aminopropyl-functionalised silica gel3-(ethylenediamino}-functionalised silica gel2-(4-(ethylenediamino)propyl-functionalised silica gel3-(diethylenetriamino)propyl-functionalised silica gel4-ethyl-benzenesulfonamide-functionalised silica gel2-(4-toluenesulfonyl hydrazino)ethyl-functionalised silica gel3-(mercapto)propyl-functionalised silica geldimethylsiloxy-functionalised silica gel or base or acid scavengers,3-(dimethylamino)propyl-functionalised silica gel3-(1,3,4,6,7,8-hexahydro-2H-pyrimido-[1,2-α]pyrimidino)propyl-functionalisedsilica gel 3-(1propyl-functionalised silica gel3-(1-morpholino)propyl-functionalised silica gel3-(1-piperazino)propyl-functionalised silica gel3-(1-piperidino)propyl-functionalised silica gel3-(4,4′-trimethyldipiperidino)propyl-functionalised silica gel2-(2-pyridyl)ethyl-functionalised silica gel3-(trimethylammonium)propyl-functionalised silica gel or the reagents,3-(1-cyclohexylcarbodiimido)propyl-functionalised silica gelTEMPO-functionalised silica gel2-(diphenylphosphino)ethyl-functionalised silica gel2-(3,4-cyclohexyldiol)propyl-functionalized silica gel3-(glycidoxy)propyl-functionalised silica gel2-(3,4-epoxycyclohexyl)propyl-functionalised silica gel1-(allyl)methyl-functionalised silica gel 4-bromopropyl-functionalisedsilica gel 4-bromophenyl-functionalised silica gel3-chloropropyl-functionalised silica gel 4-benzylchloride-functionalised silica gel 2-(carbomethoxy)propyl-functionalisedsilica gel 3-(4-nitrobenzamido)propyl-functionalised silica gel3-(ureido)propyl-functionalised silica gel or any combinations of theabove.

The use of such captive (non-labile, insoluble and/or immobilised)species, such as the foregoing, bound to an insoluble and immobilised)substrate over and/or through which the irrigant and/or wound exudatefrom, the wound dressing passes has been described hereinbefore assuitable for the means for fluid cleansing.

However, they may additionally, where appropriate, be used in any partof the apparatus that is in contact with the irrigant and/or woundexudate, but often within the dressing, for removal of materialsdeleterious to wound healing from wound.

The means for fluid cleansing may additionally, where appropriate,comprise one or more macroscopic and/or microscopic filters.

These are to retain particulates, e.g. cell debris and micro-organisms,allowing proteins and nutrients to pass through.

Alternatively, a less conventional type of two-phase system (see above),such as a dialysis unit, may be used as the means for fluid cleansing.In this type, the dialysis polymer film, sheet or membrane is not aninteger selectively permeable to materials deleterious to wound healing,such as proteases, such as serine proteases, e.g. elastase and thrombin;cysteine protease; matrix metalloproteases, e.g. collagenase; andcarboxyl (acid) proteases; endotoxins, such as lipopolysaccharides;inhibitors of angiogenesis such as thrombospondin-1 (TSP-1), plasminogenactivator inhibitor, or angiostatin (plasminogen fragment);pro-inflammatory cytokines such as tumour necrosis factor alpha (TNFα)and interleukin 1 beta (IL-1β); and oxidants, such as free radicals,e.g., e.g. peroxide and superoxide; and metal ions, e.g. iron II andiron Ill; all involved in oxidative stress on the wound bed; and basicor acidic species which adversely affect the pH in the wound exudate,such as protons.

It will however also permit components of the exudate from a woundand/or irrigant fluid that may be larger or smaller molecules, but arebeneficially involved in wound healing to pass into and through it.

In the dialysate, or preferably in one or more solid structural integerswith at least one surface in contact with the dialysate, in the meansfor fluid cleansing, there are one or more materials that can removematerials deleterious to wound healing from wound exudate, by beingantagonists to such species, for example enzymes or others, such asprotease inhibitors, such as serine protease inhibitors, such as4-(2-aminoethyl)-benzene sulphonyl fluoride (AEBSF, PefaBloc) andNα-p-tosyl-L-lysine chloromethyl ketone (TLCK) andε-aminocaproyl-p-chlorobenzylamide; cysteine protease inhibitors; matrixmetalloprotease inhibitors; and carboxyl (acid) protease inhibitors;binders and/or degraders, such as anti-inflammatory materials to bind ordestroy lipopolysaccharides, e.g. peptidomimetics; antioxidants, such as3-hydroxytyramine (dopamine), ascorbic acid (vitamin C), vitamin E andglutathione, and stable derivatives thereof, and mixtures thereof; torelieve oxidative stress on the wound bed; and chelators and/or ionexchanges, such as desferrioxamine (DFO), 3-hydroxytyramine (dopamine);and agents for the adjustment of pH in the wound exudate, such as baseor acid scavengers and/or ion exchangers, or other species, which may benon-labile, insoluble and/or immobilised) species, such as ScavengePore®phenethyl morpholine (Aldrich).

They further include peptides (including cytokines, e.g. bacterialcytokines, such as α-amino-γ-butyrolactone and L-homocarnosine); andsacrificial redox materials that are potentially or actually beneficialin promoting wound healing, such as iron III reductants; and/orregeneratable materials of this type, such as glutathione redox systems;and other physiologically active components.

In use of the two-phase system dialysis unit, of tis less conventionaltype, a broad spectrum of species will usually pass into the dialysatefrom the exudate.

Some (mainly ionic) species will pass from the dialysate into theirrigant and/or wound exudate through the dialysis polymer film, sheetor membrane that is not very selectively permeable to materialsdeleterious to wound healing.

The components of the exudate from a wound and/or irrigant fluid willdiffuse freely to and fro through it.

If (preferably) none of the dialysate is voided to waste, e.g. to acollection bag, a steady state concentration equilibrium is eventuallyset up between the dialysate and the irrigant and/or wound exudate,which is ‘topped up’ from the wound dressing.

Circulating wound fluid aids in the quicker attainment of thisequilibrium of materials beneficial in promoting wound healing.

It also returns them to the site where they can be potentially of mostbenefit, i.e. the wound bed.

The target materials deleterious to wound healing also pass into thedialysate from the exudate through the dialysis polymer film, sheet ormembrane that is not very selectively permeable to materials deleteriousto wound healing, come into contact with the appropriate antagonists,binders and/or degraders, chelators and/or ion exchangers and redoxagents, etc. in the dialysate, or preferably on one or more solidstructural integers with at least one surface in the dialysate, andunlike the other components of the exudate from a wound and/or irrigantfluid, are removed.

The cleansed fluid, still containing some materials that are beneficialin promoting wound healing, is returned to the recirculation tube.

Unlike the other components of the exudate from a wound and/or irrigantfluid the target materials are constantly removed from the dialysate,very little of these species will pass from the dialysate into theirrigant and/or wound exudate, and a steady state concentrationequilibrium is not set up, even if the species are constantly ‘toppedup’ from the wound dressing.

It is believed that circulating wound fluid aids in removal fromrecirculation of the materials deleterious to wound healing from woundexudate, whilst retaining materials that are beneficial in promotingwound healing in contact with the wound.

A particular advantage of this form of the two-phase system, is thatwhere a material that can remove materials deleterious to wound healingfrom wound exudate is (cyto)toxic or bioincompatible, or not inert toany components that are beneficial in promoting wound healing, thesystem does not allow any significant amounts of antagonist to diffusefreely out of the dialysate into the irrigant fluid. The active materialcan act beneficially on the fluid however.

The film sheet or membrane is preferably a dialysis membrane ofmolecular weight cut off (MWCO) (as conventionally defined) chosen toallow perfusion of species targeted for sequestration or destruction.

For example, sequestration of the serine protease elastase (molecularweight 25900 Dalton) would require a membrane with MWCO >25900 Dalton.

The MWCO threshold can be varied to suit each application between 1 and3000000 Dalton. Preferably, the MWCO should be as close as possible tothis weight to exclude sequestering interference by larger competitorspecies.

Both the single-phase system, such as an ultrafiltration unit, andtwo-phase system, such as a dialysis unit, may be in modular form thatis relatively easily demountable from the apparatus of the invention.The system may suitably comprise one or more such modules.

The conduits through which respectively

-   -   a) the irrigant and/or wound exudate passes from the wound        dressing and    -   b) the cleansed fluid, still containing materials that are        beneficial in promoting wound healing, is returned to the        recirculation tube, and    -   c) (in the case where the means is provided in the form of a        two-phase system, such as an dialysis unit) through which the        cleansing fluid enters and exits the means    -   preferably have means for, on module disconnection and        withdrawal,    -   i) switching off the flow and    -   i) providing an immediate fluid-tight seal or closure over the        ends of the conduits and the cooperating tubes in the rest of        the apparatus of the invention so exposed,    -   to prevent continuing passage of irrigant and/or exudate and        cleansed fluid, and cleansing fluid.

The apparatus of the invention for aspirating, irrigating and/orcleansing wounds is provided with means for bleeding the offtake and/orrecirculation tubes, such as a regulator, such as a valve or othercontrol device for bleeding fluids from the wound.

The device for moving fluid through the wound and means for fluidcleansing is used to move irrigant to the wound dressing and apply thedesired positive or negative pressure on the wound bed.

The desired balance of fluid in recirculation tube will typically beregulated by means of

-   -   a) the means for bleeding the offtake and/or recirculation        tubes,    -   b) the means for flow switching between supply and        recirculation, and/or    -   c) the means for moving fluid over the scaffold and wound bed        and through the means for fluid cleansing, as appropriate.

Thus, e.g. if

-   -   a) the apparatus for aspirating, irrigating and/or cleansing        wounds is a single-phase system, such as an ultrafiltration        unit,    -   b) the wound is not in a highly exuding state and    -   c) it is not appropriate or desired to admit fluid into the        wound from the fluid reservoir, there is no or negligible change        in the balance of fluid in recirculation.

Once it has been primed throughout, e.g. to the desired positive ornegative pressure on the wound bed, the apparatus may be operated as aclosed recirculating system.

The means for flow switching between supply and recirculation tubes isset to close the wound to the fluid reservoir via the fluid supply tube,and the means for bleeding the offtake and/or recirculation tubes arealso closed.

If

-   -   a) the apparatus for aspirating, irrigating and/or cleansing        wounds ‘is a single-phase system, such as an ultrafiltration        unit,    -   b) the wound is in a highly exuding state and/or    -   c) it is appropriate or desired to admit fluid into the wound        from the fluid reservoir,    -   there is a positive change in the balance of fluid in        recirculation.

Once it has been primed throughout, e.g. to the desired positive ornegative pressure on the wound bed, the apparatus cannot be operated asa closed recirculating system, without the pressure to the wound bedincreasing, possibly undesirably.

The means for bleeding the offtake and/or recirculation tubes must beopened to some extent to relieve positive pressure on the wound bed. Thebleed-off may be voided to waste, e.g. to a collection bag.

Materials that are beneficial in promoting wound healing may be lost tothe site where they can be potentially of most benefit, i.e. the woundbed, when the therapy is applied in this way.

However, the balance of fluid in recirculation may be routinely adjustedto minimise this undesired loss.

The factors that determine the balance of fluid in recirculation in anapparatus with a two-phase system means for fluid cleansing in the formof a dialysis unit, or a biphasic extraction unit have been describedhereinbefore in detail in connection with the operation of theapparatus. It is sufficient to note here that at some point after steadystate recirculation established through the length of the apparatus flowpath, it may be necessary that any bleed valve is opened, if overall thefluid level is increasing by transfer from the dialysate to anundesirable extent.

Other combinations, and the necessary adjustments to maintain thedesired balance of fluid in recirculation tube by means of

-   -   a) the means for bleeding the offtake and/or recirculation        tubes,    -   b) the means for flow switching between supply and        recirculation, and/or    -   c) the means for moving fluid will be apparent to the skilled        person.

The outlet from the means for bleeding the offtake and/or recirculationtubes may be collected and monitored and used to diagnose the status ofthe wound and/or its exudate.

The waste reservoir may be of any conventional type, e.g. a tube, bag(such as a bag typically used as an ostomy bag), chamber, pouch or otherstructure, e.g. of polymer film, which can contain the irrigant fluidthat has been bled off. In all embodiments of the apparatus, the typeand material of the waste reservoir will be largely determined by itsfunction. To be suitable for use, the material need only befluid-impermeable once in use, and flexible.

Examples of suitable materials for the fluid reservoir include syntheticpolymeric materials, such as polyolefins, such as poly (vinylidenechloride).

Suitable materials for the present purpose also include polyethylene,e.g. high-density polyethylene, polypropylene, copolymers thereof, forexample with vinyl acetate and mixtures thereof.

In a second aspect of the present invention there is provided aconformable wound dressing, characterised in that it comprises

-   -   a backing layer with a wound-facing face which is capable of        forming a relatively fluid-tight seal or closure over a wound        and has    -   at least one inlet pipe for connection to a fluid supply tube,        which passes through and/or under the wound-facing face, and    -   at least one outlet pipe for connection to a fluid offtake tube,        which passes through and/or under the wound-facing face,    -   the point at which the or each inlet pipe and the or each outlet        pipe passes through and/or under the wound-facing face forming a        relatively fluid-tight seal or closure over the wound.

Examples of suitable forms of such wound dressings are as described byway of example hereinbefore.

The dressing is advantageously provided for use in a bacteria-proofpouch.

The conformable wound dressing of the second aspect of the presentinvention is used for aspirating, irrigating and/or cleansing woundswithin the scope of the present invention in conjunction with abiodegradable scaffold, which permits fluid supply towards the wound bedfrom the wound dressing.

Thus, according to a third aspect of the present invention there isprovided a dressing assembly for wound aspiration and/or irrigationtherapy, characterised in that it comprises a dressing of the secondaspect of the present invention and a biodegradable scaffold, which islocated under the wound dressing in use.

It is an object of the present invention

-   -   c) to obviate at least some of the disadvantages of known        aspiration and/or irrigation therapies, and    -   d) to provide a system of therapy which        -   i) can remove materials deleterious to wound healing from            wound exudate, whilst retaining materials that are            beneficial in promoting wound healing in contact with the            wound bed, and/or        -   ii) which allows fluids containing active amounts of            materials that are beneficial in promoting wound healing to            pass into and/or through the wound in contact with the            scaffold and the wound bed.

Thus, in a third aspect of the present invention there is provided amethod of treating wounds to promote wound healing using the apparatusfor aspirating, irrigating and/or cleansing wounds of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only withreference to the accompanying drawings in which:

FIG. 1 is a schematic view of an apparatus for aspirating, irrigatingand/or cleansing a wound according to the first aspect of the presentinvention. It has a single-phase system means for fluid cleansing in theform of an ultrafiltration unit.

FIG. 2 is a schematic view of an apparatus for aspirating, irrigatingand/or cleansing a wound according to the first aspect of the presentinvention. It has a two-phase system means for fluid cleansing in theform of a dialysis unit, or a biphasic extraction unit.

FIGS. 3 a and 3 b are cross-sectional views of conformable wounddressings, of the second aspect of the present invention for aspiratingand/or irrigating wounds. In these, FIG. 3 a is a cross-sectional planview of the wound dressings, and FIG. 3 b is a cross-sectional side viewof the wound dressings.

FIGS. 4 a and 4 b are cross-sectional views of conformable wounddressings, of the second aspect of the present invention for aspiratingand/or irrigating wounds. In these, FIG. 4 a is a cross-sectional planview of the wound dressing, and FIG. 4 b is a cross-sectional side viewof the wound dressing.

FIGS. 5 a and 5 b are cross-sectional views of conformable wounddressings, of the second aspect of the present invention for aspiratingand/or irrigating wounds. In these, FIG. 5 a is a cross-sectional planview of the wound dressing, and FIG. 5 b is a cross-sectional side viewof the wound dressing.

FIGS. 6 a and 6 b are cross-sectional views of conformable wounddressings, of the second aspect of the present invention for aspiratingand/or irrigating wounds. In these, FIG. 6 a is a cross-sectional planview of the wound dressing, and FIG. 6 b is a cross-sectional side viewof the wound dressing.

FIGS. 7 a and 7 b are cross-sectional views of conformable wounddressings, of the second aspect of the present invention for aspiratingand/or irrigating wounds. In these, FIG. 7 a is a cross-sectional planview of the wound dressing, and FIG. 7 b is a cross-sectional side viewof the wound dressing.

FIGS. 8 a, 8 b, 8 c and 8 d are various views of inlet and outletmanifold layouts for the wound dressings of the second aspect of thepresent invention for respectively delivering fluid to, and collectingfluid from, the wound.

FIGS. 9 a and 9 b are various views of inlet and outlet manifold layoutsfor the wound dressings of the second aspect of the present inventionfor respectively delivering fluid to, and collecting fluid from, thewound.

FIGS. 10 a, 10 b, and 10 c are various views of inlet and outletmanifold layouts for the wound dressings of the second aspect of thepresent invention for respectively delivering fluid to, and collectingfluid from, the wound.

FIG. 11 is a schematic view of an apparatus for aspirating, irrigatingand/or cleansing a wound according to the first aspect of the presentinvention. It has a single-phase system means for fluid cleansing in theform of an ultrafiltration unit.

FIG. 12 is a schematic view of an apparatus for aspirating, irrigatingand/or cleansing a wound according to the first aspect of the presentinvention. It has a two-phase system means for fluid cleansing in theform of a dialysis unit, or a biphasic extraction unit.

FIGS. 13 a and 13 b are views of conformable wound dressings of thesecond aspect of the present invention for aspirating and/or irrigatingwounds.

FIG. 14 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIG. 15 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIGS. 16 a and 16 b are views of a conformable wound dressing of thesecond aspect of the present invention for aspirating and/or irrigatingwounds.

FIG. 17 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIGS. 18 a and 18 b are views of a conformable wound dressing of thesecond aspect of the present invention for aspirating and/or irrigatingwounds.

FIG. 19 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIG. 20 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIG. 21 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIG. 22 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIG. 23 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIG. 24 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIG. 25 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIG. 26 is a view of a conformable wound dressing of the second aspectof the present invention for aspirating and/or irrigating wounds.

FIGS. 27 a and 27 b are views of a conformable wound dressing of thesecond aspect of the present invention for aspirating and/or irrigatingwounds.

FIG. 28 is a schematic view of an apparatus for aspirating, irrigatingand/or cleansing a wound according to the first aspect of the presentinvention. It has a single-phase system means for fluid cleansing in theform of an ultrafiltration unit.

In all of the Figures, whether showing a schematic view of an apparatusfor aspirating, irrigating and/or cleansing a wound according to thefirst aspect of the invention, or a view of conformable wound dressingsof the second aspect of the present invention, a biodegradable scaffoldis located under the wound dressing in use in contact with andconforming to the wound bed. It is omitted throughout for clarity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the apparatus (1) for aspirating, irrigating and/orcleansing wounds comprises a conformable wound dressing (2), having abacking layer (3) which is capable of forming a relatively fluid-tightseal or closure (4) over a wound (5) and one inlet pipe (6) forconnection to a fluid supply tube (7), which passes through thewound-facing face of the backing layer (5) at (8), and one outlet pipe(9) for connection to a fluid offtake tube (10), which passes throughthe wound-facing face at (11), the points (8), (11) at which the inletpipe and the outlet pipe passes through and/or •under the wound-facingface forming a relatively fluid-tight seal or closure over the wound,and a biodegradable scaffold (111) located under the backing layer andconfigured to be placed in contact with a wound bed in use; the inletpipe being connected via means for flow switching between supply andrecirculation, here a T-valve (14), by the fluid supply tube (7) to afluid reservoir (12) and to a fluid recirculation tube (13) having ameans for bleeding the tube, here a bleed T-valve (16) to waste, e.g. toa collection bag (not shown), the outlet pipe (9) being connected to afluid offtake tube (15), connected in turn to means for fluid cleansing(17), here in the form of an ultrafiltration unit, connected to theinlet pipe (6) via the fluid recirculation tube (13) and T-valve (14),and a device for moving fluid through the wound and means for fluidcleansing (17), here a peristaltic pump (18), e.g. preferably a smallportable peristaltic pump, acting on the fluid circulation tube (13)with the peripheral rollers on its rotor (not shown) to apply a lownegative pressure on the wound.

The ultrafiltration unit (17) is a single-phase system. In this thecirculating fluid from the wound and the fluid reservoir passes througha self-contained system in which materials deleterious to wound healingare removed and the cleansed fluid, still containing materials that arebeneficial in promoting wound healing, is returned via the recirculationtube to the wound bed.

(In a variant of this apparatus, there are two inlet pipes (6), whichare connected respectively to a fluid supply tube (7) and fluidrecirculation tube (13), respectively having a first valve (19) foradmitting fluid into the wound from the fluid reservoir (12) and asecond valve (20) for admitting fluid into the wound from therecirculation tube. Usually in use of the apparatus, when the firstvalve (19) is open, the second valve (20) is shut, and vice versa.)

In use of the apparatus (1), the valve (16) is opened to a collectionbag (not shown), and the T-valve (14) is turned to admit fluid from thefluid reservoir to the wound dressing through the fluid supply tube (7)and inlet pipe (6).

(In the variant of this apparatus having two inlet pipes (6), which areconnected respectively to a fluid supply tube (7) and fluidrecirculation tube (13), the first valve (19) for admitting fluid intothe wound from the fluid reservoir (12) is opened and the second valve(20) is shut, and vice versa.) The pump (18) is started to nip the fluidrecirculation tube (13) with the peripheral rollers on its rotor (notshown) to apply a low positive pressure on the wound. It is allowed torun until the apparatus is primed throughout the whole length of theapparatus flow path and excess fluid is voided to waste via the bleedT-valve (16) into the collection bag (not shown).

The T-valve (14) is then turned to switch from supply and recirculation,i.e. is set to close the wound to the fluid reservoir (12) but to admitfluid into the wound from the fluid recirculation tube (13), and thebleed T-valve (16) is simultaneously closed.

(In a variant of this apparatus, there are two inlet pipes ^(o)(6),which are connected respectively to a fluid supply tube (7) and fluidrecirculation tube (13).

In operation of this variant, the first valve (19) is closed and arecirculating system set up by opening the second valve (20) foradmitting fluid into the wound from the recirculation tube (13).

The circulating fluid from the wound and the fluid reservoir (12) passesthrough the ultrafiltration unit (17).

Materials deleterious to wound healing are removed and the cleansedfluid, till containing materials that are beneficial in promoting woundhealing, is returned via the recirculation tube (13) to the wound bed.

The recirculation of fluid may be continued as long as desired.

Switching between supply and recirculation is then reversed, by turningthe T-valve (14) to admit fluid from the fluid reservoir to the wounddressing through the fluid supply tube (7) and inlet pipe (6).

(In the variant of this apparatus having two inlet pipes (6), which areconnected respectively to a fluid supply tube (7) and fluidrecirculation tube (13), the first valve (19) for admitting fluid intothe wound from the fluid reservoir (12) is opened and the second valve(20) is shut, and vice versa.) The bleed valve (16) is simultaneouslyopened, so that fresh fluid flushes the recirculating system.

The running of the pump (18) may be continued until the apparatus isflushed, when it and the fluid recirculation is stopped.

If, e.g. the wound is in a highly exuding state, there is a positivechange in the balance of fluid in recirculation. It may be necessary tobleed fluid from recirculation, by opening the bleed T-valve (16) tobleed fluid from the recirculation tube (13).

Referring to FIG. 2, the apparatus (21) is a variant of that of FIG. 1,with identical, and identically numbered, components, except for themeans for fluid cleansing, which is in the form of a two-phase system,here a dialysis unit (23).

In this, there is one system through which the circulating fluid fromthe wound and the fluid reservoir passes and from which deleteriousmaterials are removed by selectively permeable contact with a secondsystem, through which passes a cleansing fluid.

The dialysis unit (23) thus has an internal polymer film, sheet ormembrane (24), selectively permeable to materials deleterious to woundhealing, which divides it into

-   -   a) a first chamber (25), through which passes a cleansing fluid        across one surface of the polymer film, sheet- or membrane, and    -   b) a second chamber (26), through which passes the circulating        fluid from the wound and the fluid • reservoir (12), and from        which deleterious materials are removed

The dialysis unit (23) thus has a dialysate inlet pipe (28) connectingto a dialysate supply tube (29) which passes to a peristaltic pump (38),e.g. preferably a small portable peristaltic pump, acting on thedialysate supply tube (29). with the peripheral rollers on its rotor(not shown) to supply cleansing fluid across the surface of the polymerfilm, sheet or membrane (28) in the first chamber (25) from a dialysatereservoir (not shown) via a valve (34).

The dialysis unit (27) also has a dialysate outlet pipe (30) connectingto a dialysate outlet tube (31) which passes to waste via a second bleedT-valve (36) into, e.g. a collection bag (not shown).

Operation of this apparatus is similar to that of FIG. 1, except for thedialysis unit (27), in that at some point after the irrigation system isprimed and steady state recirculation established through the length ofthe apparatus flow path, the valve (34) and second bleed valve (36) areopened.

The pump (38) is started to nip fluid dialysate tube (37) with theperipheral rollers on its rotor (not shown) to pump cleansing fluid tothe first chamber from a dialysate reservoir (not shown) and out towaste via the bleed valve (36) into the collection bag (not shown).

The dialysis unit (27) is a module (or scrubbing cartridge) with asubstrate that changes colour to indicate the presence of detrimentalfactors in the cleansed fluid, and that the scrubbing cartridge isexhausted and should be renewed.

Referring to FIGS. 3 a to 6 b, each dressing (41) is in the form of aconformable body defined by a microbe-impermeable film backing layer(42) with a uniform thickness of 25 micron, with a wound-facing face(43) which is capable of forming a relatively fluid-tight seal orclosure over a wound.

The backing layer (42) extends in use on a wound over the skin aroundthe wound.

On the proximal face of the backing layer (43) on the overlap (44), itbears an adhesive film (45), to attach it to the skin sufficiently tohold the wound dressing in place in a fluid-tight seal around theperiphery of the wound-facing face (43) of the wound dressing.

There is one inlet pipe (46) for connection to a fluid supply tube (notshown), which passes through and/or under the wound-facing face (43),and one outlet pipe (47) for connection to a fluid offtake tube (notshown), which passes through and/or under the wound-facing face (43), abiodegradable scaffold (111) is located under the rest of the dressingand placed in contact with a wound bed in use.

Referring to FIGS. 3 a and 3 b, one form of the dressing is providedwith a wound filler (48) under a circular backing layer (42).

This comprises a generally frustroconical, toroidal conformable hollowbody, defined by a membrane (49) which is filled with a fluid, here airor nitrogen, that urges it to the wound shape. The filler (48) ispermanently attached to the backing layer with an adhesive film (notshown) or by heat-sealing.

The inlet pipe (46) and outlet pipe (47) are mounted centrally in thebacking layer (42) above the central tunnel (50) of the toroidal hollowbody (48) and each passes through the backing layer (42).

Each extends in pipes (51) and (52) respectively through the tunnel (50)of the toroidal hollow body (48) and then radially in diametricallyopposite directions under the body (48).

A biodegradable scaffold (111) is located under the rest of the dressingand placed in contact with a wound bed in use.

This form of the dressing is a more suitable layout for deeper wounds.

Referring to FIGS. 4 a and 4 b, a more suitable form for shallowerwounds is shown.

This comprises a circular backing layer (42) and a circular upwardlydished first membrane (61) with apertures (62) that is permanentlyattached to the backing layer (42) by heat-sealing to form a circularpouch (63).

The pouch (63) communicates with the inlet pipe (46) through a hole(64), and thus effectively forms an inlet pipe manifold that deliversthe circulating fluid directly to the wound when the dressing is in use.

An annular second membrane (65) with openings (66) is permanentlyattached to the backing layer (42) by heat-sealing to form an annularchamber (67) with the layer (42).

The chamber (67) communicates with the outlet pipe (47) through anorifice (68), and thus effectively forms an outlet pipe manifold thatcollects the fluid directly from the wound when the dressing is in use.

A biodegradable scaffold (111) is located under the rest of the dressingand placed in contact with a wound bed in use.

Referring to FIGS. 5 a and 5 b, a variant of the dressing of FIGS. 4 aand 4 b that is a more suitable form for deeper wounds is shown.

This comprises a circular backing layer (42) and a filler (69), in theform of an inverted frustroconical, solid integer, here a resilientelastomeric foam, formed of a thermoplastic, or preferably across-linked plastics foam.

It is permanently attached to the backing layer (43), with an adhesivefilm (not shown) or by heat-sealing.

A circular upwardly dished sheet (70) lies under and conforms to, but isa separate structure, permanently unattached to, the backing layer (42)and the solid integer (69).

A circular upwardly dished first membrane (71) with apertures (72) ispermanently attached to the sheet (70) by heat-sealing to-form acircular pouch (73) with the sheet (70).

The pouch (73) communicates with the inlet pipe (46) through a hole(74), and thus effectively forms an inlet pipe manifold that deliversthe circulating fluid directly to the wound when the dressing is in use.

An annular second membrane (75) with openings (76) is permanentlyattached to the sheet (70) by heat-sealing to form an annular chamber(77) with the sheet (70).

The chamber (77) communicates with the outlet pipe (77) through anorifice (78), and thus effectively forms an outlet pipe manifold thatcollects the fluid directly from the wound when the dressing is in use.

A biodegradable scaffold (111) is located under the rest of the dressingand placed in contact with a wound bed in use.

Alternatively, where appropriate the dressing may be provided in a formin which the circular upwardly dished sheet (70) functions as thebacking layer and the solid filler (69) sits on the sheet (70) as thebacking layer, rather than under it. The filler (69) is held in placewith an adhesive film or tape, instead of the backing layer (42).

Referring to FIGS. 6 a and 6 b, a dressing that is a more suitable formfor deeper wounds is shown.

This comprises a circular backing layer (42) and a filler (79), in theform of an inverted generally hemispherical integer, here a resilientelastomeric foam or a hollow body filled with a fluid, here a gel thaturges it to the wound shape, and permanently attached to the backinglayer with an adhesive film (not shown) or by heat-sealing.

The inlet pipe (46) and outlet pipe (47) are mounted peripherally in thebacking layer (42). A circular upwardly dished sheet (80) lies under andconforms to, but is a separate structure, permanently unattached to, thebacking layer (42) and the filler (79).

A circular upwardly dished bilaminate membrane (81) has a closed channel(82) between its laminar components, with perforations (83) along itslength on the outer surface (84) of the dish formed by the membrane (81)and an opening (85) at the outer end of its spiral helix, through whichthe channel (82) communicates with the inlet pipe (46), and thuseffectively forms an inlet pipe manifold that delivers the circulatingfluid directly to the wound when the dressing is in use.

The membrane (81) also has apertures (86) between and along the lengthof the turns of the channel (82).

The inner surface (87) of the dish formed by the membrane (81) ispermanently attached at its innermost points (88) with an adhesive film(not shown) or by heat-sealing to the sheet (80). This defines a matingclosed spirohelical conduit (89).

At the outermost end of its spiral helix, the conduit (89) communicatesthrough an opening (90) with the outlet pipe (47) and is thuseffectively an outlet manifold to collect the fluid directly from thewound via the apertures (86).

A biodegradable scaffold (111) is located under the rest of the dressingand placed in contact with a wound bed in use.

Referring to FIGS. 7 a and 7 b, one form of the dressing is providedwith a circular backing layer (42). A first (larger) invertedhemispherical membrane (92) is permanently attached centrally to thelayer (42) by heat-sealing to form a hemispherical chamber (94) with thelayer (42). A second (smaller) concentric hemispherical membrane (93)within the first is permanently attached to the layer (42) byheat-sealing to form a hemispherical pouch (95).

A biodegradable scaffold (111) is located under the rest of the dressingand placed in contact with a wound bed in use.

The pouch {95) communicates with the inlet pipe (46) and is thuseffectively an inlet manifold, from which pipes (97) radiatehemispherically and run to the scaffold to end in apertures (98). Thepipes (97) deliver the circulating fluid directly to the scaffold viathe apertures (98).

The chamber (94) communicates with the outlet pipe (47) and is thuseffectively an outlet manifold from which tubules (99) radiatehemispherically ad run to the scaffold to end in openings (100). Thetubules (99) collect the fluid directly from the wound via the openings(100).

Referring to FIGS. 8 a to 8 d, one form of the dressing is provided witha square backing layer (42).

A biodegradable scaffold (111) is located under the rest of the dressingand placed in contact with a wound bed in use.

A first tube (101) extends from the inlet pipe (46), and a second tube(102) extends from the outlet pipe (47) at the points at which they passthrough the backing layer, to run over the scaffold. These pipes (101),(102) have a blind bore with orifices (103), (104) along the pipes(101), (102), which respectively form an inlet pipe or outlet pipemanifold that delivers the circulating fluid directly to the scaffold orcollects the fluid directly from the wound respectively via theorifices.

In FIGS. 8 a and 8 d, one layout of each of the pipes (101), (102) asinlet pipe and outlet pipe manifolds is a spiral.

In FIG. 8 b, the layout is a variant of that of FIGS. 8 a and 8 b, withthe layout of the inlet manifold (101) being a full or partial torus,and the outlet manifold (102) being a radial pipe.

Referring to FIG. 8 c, there is shown another suitable layout in whichthe inlet manifold (101) and the outlet manifold (102) run alongsideeach other over the scaffold in a boustrophedic pattern, i.e. in themanner of ploughed furrows.

Referring to FIGS. 9 a to 9 d, there are shown other suitable layoutsfor deeper wounds, which are the same as shown in FIGS. 8 a to 8 d.

A biodegradable scaffold (111) is located under the rest of the dressingand placed in contact with a wound bed in use.

The square backing layer (42) however has a wound filler (110) under,and permanently attached to, the backing layer (42), with an adhesivefilm (not shown) or by heat-sealing, which is an inverted hemisphericalsolid integer, here a resilient elastomeric foam, formed of athermoplastic, preferably a cross-linked plastics foam.

Under the latter is a circular upwardly dished sheet (111) whichconforms to, but is a separate structure, permanently unattached to, thesolid filler (110). Through the sheet (111) pass the inlet pipe (46) andthe outlet pipe (47), to run over the scaffold. These pipes (101), (102)again have a blind bore with orifices (103), (104) along the pipes(101), (102).

Alternatively (as in FIGS. 5 a and 5 b), where appropriate the dressingmay be provided in a form in which the circular upwardly dished sheet(111) functions as the backing layer and the solid filler (110) sits onthe sheet (42) as the backing layer, rather than under it. The filler(110) is held in place with an adhesive film or tape, instead of thebacking layer (42).

In FIGS. 10 a to 10 c, inlet and outlet manifolds for the wounddressings for respectively delivering fluid to, and collecting fluidfrom, the wound, are formed by slots in and apertures through layerspermanently attached to each other in a stack.

Thus, in FIG. 10 a there is shown an exploded isometric view of an inletmanifold and outlet manifold stack (120) of five square coterminousthermoplastic polymer layers, being first to fifth layers (121) to(125), each attached with an adhesive film (not shown) or byheat-sealing to the adjacent layer in the stack (120).

The topmost (first) layer (121) (which is the most distal in thedressing in use) is a blank square capping layer.

The next (second) layer (122), shown in FIG. 10 b out of the manifoldstack (120), is a square layer, with an inlet manifold slot (126)through it. The slot (126) runs to one edge (127) of the layer (122) forconnection to a mating end of a fluid inlet tube ((not shown), andspreads into four adjacent branches (128) in a parallel array withspaces therebetween.

The next (third) layer (123) is another square layer, with inletmanifold apertures (129) through the layer (123) in an array such thatthe apertures (129) are in register with the inlet manifold slot (126)through the second layer (122) (shown in FIG. 10 b).

The next (fourth) layer (124), shown in FIG. 10 c out of the manifoldstack (120), is another square layer, with inlet manifold apertures(130) through the layer (124) in an array such that the apertures (130)are in register with the apertures (129) through the third layer (123).

It also has an outlet manifold slot (131) through it.

The slot (131) runs to one edge (132) of the layer (124) on the oppositeside of the manifold stack (120) from the edge (127) of the layer (122),for connection to a mating end of a fluid outlet tube (not shown).

It spreads into three adjacent branches (133) in a parallel array in thespaces between the apertures (130) in the layer (124) and in registerwith the spaces between the apertures (129) in the layer (122).

The final (fifth) layer (125) is another square layer, with inletmanifold apertures (134) through the layer (125) in an array such thatthe apertures (134) are in register with the inlet manifold apertures(130) through the fourth layer (124) (in turn in register with theapertures (129) through the third layer (123).

It also has outlet manifold apertures (135) in the layer (125) in anarray such that the apertures (135) are in register with the outletmanifold slot (131) in the fourth layer (124).

It will be seen that, when the layers (121) to (125) are attachedtogether to form the stack (120), the topmost (first) layer (121), theinlet manifold slot (126) through the second layer (122), and the thirdlayer (123) cooperate to form an inlet manifold—in the second layer(122), which is in use is connected to a mating end of a fluid inlettube (not shown).

The inlet manifold slot (126) through the second layer (122), and theinlet manifold apertures (129), (130) and (134) through the layers(123), (124) and (125), all being mutually in register, cooperate toform inlet manifold conduits though the third to fifth layers (123),(124) and (125) between the inlet manifold in the second layer (122) andthe proximal face (136) of the stack (120).

The third layer (121), the outlet manifold slot (131) through the fourthlayer (124), and the fifth layer (125) cooperate to form an outletmanifold in the fourth layer (124), which is in use is connected to amating end of a fluid outlet tube (not shown).

The outlet manifold slot (131) through the fourth layer (124), and theoutlet manifold apertures (135) through the fifth layer (125), beingmutually in register, cooperate to form outlet manifold conduits thoughthe fifth layer (125) between the outlet manifold in the fourth layer(124) and the proximal face (136) of the stack (120).

A biodegradable scaffold (111) is located under the rest of the dressingand placed in contact with a wound bed in use.

Referring to FIG. 11, the apparatus (1) for aspirating, irrigatingand/or cleansing wounds is a variant of the apparatus (1) of FIG. 1.

It has bypass (711) around the pump (17), as a protection of the pumpagainst any blockage in the system.

It is activated automatically by appropriate means, e.g. it is normallyblocked by a bursting disc (not shown), or a pressure-activatedmotorised valve.

An alternative to the by-pass (711) is a pressure sensor in the systemthat will detect excessive load or pressure, and shut down the pump.

Referring to FIG. 12, the apparatus (1) for aspirating, irrigatingand/or cleansing wounds is a variant of the apparatus (1) of FIG. 2.

The latter is a two-phase system with a dialysis unit (21), but is onein which dialytic fluid passes only once across the surface of thedialytic membrane (28) in the first chamber (25) from a dialysatereservoir (not shown) to waste via a second bleed T-valve (36) into,e.g. a collection bag (not shown).

This variant has a dialysate recirculation tube (811) running between afirst T-valve (816) on the inlet side of the dialysate pump (23) and asecond T-valve (817) to permit the pump (23) to recirculate thedialysate once the circuit is primed in multiple passes through thedialysis unit (21).

The operation of the system will be apparent to the skilled person.

Referring to FIGS. 13 a to 15, these forms of the dressing are providedwith a wound filler (348) under a circular backing layer (342).

This comprises respectively a generally downwardly domed or toroidal, oroblately spheroidal conformable hollow body, defined by a membrane (349)which is filled with a fluid, here air or nitrogen, that urges it to thewound shape.

The filler (348) is permanently attached to the backing layer via a boss(351), which is e.g. heat-sealed to the backing layer (342).

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)are mounted centrally in the boss (351) in the backing layer (342) abovethe hollow body (348). The inflation inlet pipe (350) communicates withthe interior of the hollow body (348), to permit inflation of the body(348).

The inlet pipe (346) extends in a pipe (352) effectively through thehollow body (348). The outlet pipe (347) extends radially immediatelyunder the backing layer (342).

In FIG. 13 a, the pipe (352) communicates with an inlet manifold (353),formed by a membrane (361) with apertures (362) that is permanentlyattached to the filler (348) by heat-sealing. It is filled with foam(363) formed of a suitable material, e.g. a resilient thermoplastic.Preferred materials include reticulated filtration polyurethane foamswith small apertures or pores.

In FIG. 14, the outlet pipe (347) communicates with a layer of foam(364) formed of a suitable material, e.g. a resilient thermoplastic.Again, preferred materials include reticulated filtration polyurethanefoams with small apertures or pores.

In all of FIGS. 13 a, 13 b, 14 and 15, in use, the pipe (346) ends inone or more openings that deliver the irrigant fluid directly from thewound bed over an extended area.

Similarly, the outlet pipe (347) effectively collects the fluid radiallyfrom the wound periphery when the dressing is in use.

Referring to FIGS. 16 a and 16 b, the dressing is also provided with awound filler (348) under a circular backing layer (342).

This also comprises a generally toroidal conformable hollow body,defined by a membrane (349) which is filled with a fluid, here air ornitrogen, that urges it to the wound shape. The filler (348) may bepermanently attached to the backing layer (342) via a first boss (351)and a layer of foam (364) formed of a suitable material, e.g. aresilient thermoplastic. Again, preferred materials include reticulatedfiltration polyurethane foams with small apertures or pores.

The first boss (351) and foam layer (364) are respectively heat-sealedto the backing layer (342) and the boss (351).

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)are mounted centrally in the first boss (351) in the backing layer (342)above the toroidal hollow body (348).

The inflation inlet pipe (350), inlet pipe (346) and outlet pipe •(347)respectively each extend in a pipe (353), (354) and (355} through acentral tunnel (356) in the hollow body (348) to a second boss (357)attached to the toroidal hollow body (348).

The pipe (353) communicates with the interior of the hollow body (348),to permit inflation of the body (348). The pipe (354) extends radiallythrough the second boss (357) to communicate with an inlet manifold(352), formed by a membrane (361) that is permanently attached to thefiller (348) by heat-sealing in the form of a reticulated honeycomb withopenings (362) that deliver the irrigant fluid directly to the wound bedover an extended area. The pipe (355) collects the fluid flowingradially from the wound centre when the dressing is in use.

This form of the dressing is a more suitable layout for deeper wounds

In FIG. 17, the dressing is similar to that of FIGS. 16 a and 16 b,except that the toroidal conformable hollow body, defined by a membrane(349), is filled with a fluid, here a solid particulates, such asplastics crumbs or beads, rather than a gas, such as air or an inertgas, such as nitrogen or argon, and the inflation inlet pipe (350) andpipe (353) are omitted from the central tunnel (356).

Examples of contents for the body (348) also include gels, such assilicone gels or preferably cellulosic gels, for example hydrophiliccross-linked cellulosic gels, such as Intrasite™ cross-linked materials.Examples also include aerosol foams, and set aerosol foams, e.g.CaviCare™ foam.

Referring to FIGS. 18 and 19, another form for deeper wounds is shown.This comprises a circular backing layer (342) and a chamber (363) in theform of a deeply indented disc much like a multiple Maltese cross or astylised rose.

This is defined by an upper impervious membrane (361) and a lower porousfilm (362) with apertures (364) that deliver the irrigant fluid directlyfrom the wound bed over an extended area.

A number of configurations of the chamber (363) are shown, all of whichare able to conform well to the wound bed by the arms closing in andpossibly overlapping in insertion into the wound.

In a particular design of the chamber (363), shown lowermost, one of thearms extended and provided with an inlet port at the end of the extendedarm. This provides the opportunity for coupling and decoupling theirrigant supply remote from the dressing and the wound in use.

An inlet pipe (346) and outlet pipe (347) are mounted centrally in aboss (351) in the backing layer (342) above the chamber (363). The inletpipe (346) is permanently attached to, and communicate with the interiorof, the chamber (363), which thus effectively forms an inlet manifold.The space above the chamber (363) is filled with a loose gauze packing(364).

In FIG. 18, the outlet pipe (347) collects the fluid from the interiorof the dressing from just under the wound-facing face (343) of thebacking layer (342).

A variant of the dressing of FIGS. 18 a and 18 b is shown in FIG. 19.The outlet pipe (347) is mounted to open at the lowest point of thespace above the chamber (363) into a piece of foam (374).

In FIG. 20, the dressing is similar to that of FIGS. 13 a and 13 b,except that the inlet pipe (352) communicates with an inlet manifold(353), formed by a membrane (361) with apertures (362), over the uppersurface of the generally downwardly domed wound hollow filler (348),rather than through it.

In FIG. 22, the dressing is similar to that of FIG. 14, with theaddition of an inlet manifold (353), formed by a membrane (361) withapertures (362), over the lower surface of the generally downwardlydomed annular wound hollow filler.

In FIG. 21, the generally downwardly domed annular wound hollow filleris omitted.

Referring to FIG. 23, another form for deeper wounds is shown. An inletpipe (346) and outlet pipe (347) are mounted centrally in a boss (351)in the backing layer (342) above a sealed-off foam filler (348). Theinlet pipe (346) is permanently attached to and passes through thefiller (348) to the wound bed. The outlet pipe (347) is attached to andcommunicates with the interior of, a chamber (363) defined by a porousfoam attached to the upper periphery of the filler (348). The chamber(63) thus effectively forms an outlet manifold.

In FIG. 24, the foam filler (348) is only partially sealed-off. Theinlet pipe (346) is permanently attached to and passes through thefiller (348) to the wound bed. The outlet pipe (347) is attached to andcommunicates with the interior of the foam of the filler (348). Fluidpasses into an annular gap (349) near the upper. periphery of the filler(348) into the foam, which thus effectively forms an outlet manifold.

FIGS. 25 and 26 show dressings in which the inlet pipe (346) and outletpipe (347) pass through the backing layer (342).

In FIG. 25, they communicates with the interior of a porous bag filler(348) defined by a porous film (369) and filled with elasticallyresilient plastics bead or crumb.

In FIG. 26, they communicate with the wound space just below a foamfiller (348). The foam (348) may CaviCare™ foam, injected and formed insitu around the pipes (346) and (347).

Referring to FIGS. 27 a and 27 b, another form for deeper wounds isshown. This comprises a circular, or more usually square or rectangularbacking layer (342) and a chamber (363) in the form of a deeply indenteddisc much like a multiple Maltese cross or a stylised rose.

This is defined by an upper impervious membrane (361) and a lower porousfilm (362) with apertures (364) that deliver the irrigant fluid directlyto the wound bed over an extended area, and thus effectively forms aninlet manifold.

Three configurations of the chamber (363) are shown in FIG. 27 b, all ofwhich are able to conform well to the wound bed by the arms closing inand possibly overlapping in insertion into the wound.

The space above the chamber (363) is filled with a wound filler (348)under the backing layer (342). This comprises an oblately spheroidalconformable hollow body, defined by a membrane (349) that is filled witha fluid, here air or nitrogen, that urges it to the wound shape.

A moulded hat-shaped boss (351) is mounted centrally on the upperimpervious membrane (361) of the chamber (363). It has three internalchannels, conduits or passages through it (not shown), each with entryand exit apertures. The filler (348) is attached to the membrane (361}of the chamber (363} by adhesive, heat welding or a mechanical fixator,such as a cooperating pin and socket.

An inflation inlet pipe (350). inlet pipe (346} and outlet pipe (347)pass under the edge of the proximal face of the backing layer (342) ofthe dressing, and extend radially immediately under the filler (348) andover the membrane (361) of the chamber (363} to each mate with an entryaperture in the boss (351).

An exit to the internal channel, conduit. or passage through it thatreceives the inflation inlet pipe (350) communicates with the interiorof the hollow filler (348), to permit inflation.

An exit to the internal channel, conduit or passage that receives theinlet pipe (346) communicates with the interior of the chamber (363) todeliver the irrigant fluid via the chamber (363) to the wound bed overan extended area.

Similarly, an exit to the internal channel, conduit or passage thatreceives the outlet pipe (347) communicates with the space above thechamber (363) and under the wound filler (348), and collects flow ofirrigant and/or wound exudate radially from the wound periphery.

Referring to FIG. 28, the apparatus (1) for aspirating, irrigatingand/or cleansing wounds is a major variant of the apparatus shown inFIG. 1.

The device for moving fluid through the wound and means for fluidcleansing (17) in FIG. 1 is a peristaltic pump (18), e.g. preferably asmall portable peristaltic pump, acting on the fluid circulation tube(13) downstream of the dressing (2) to apply a low negative pressure onthe wound.

In the apparatus (1) shown in FIG. 28, the peristaltic pump (18) isreplaced by:

-   -   a) a peristaltic pump (926) acting on the fluid supply tube (7)        upstream of the dressing (2), and    -   b) a vacuum pump assembly (918) with pressure regulating means,        acting on the fluid circulation tube (13) downstream of the        dressing (2), to apply an overall low negative pressure in the        wound space.

The vacuum pump assembly comprises a tank (911) with an inlet tube (912)connecting to the fluid circulation tube (13) and communicating with theupper part of the tank (911), a waste tube (913) connecting to a wastepump (914) with waste bag (915) and communicating with the lower part ofthe tank (911), a pump tube (917) connecting to a vacuum pump (918) andcommunicating with the upper part of the tank (911), and connecting viathe fluid circulation tube (13) to the means for cleansing (17) andcommunicating with the lower part of the tank (911).

The vacuum pump (918) is controlled by a pressure feedback regulator(919) through an electrical line (920), the regulator receiving signalsfrom a tank sensor (921) in the upper part of the tank (911), and adressing sensor (922) in the wound space respectively via lines (923)and (924).

The waste pump (914) is controlled by a waste level feedback regulator(929) the regulator receiving signals from a tank sensor with electricalline (930) in the middle part of the tank (911).

The vacuum pump (918) either acts as a valve so that the pump tube 917connecting to the vacuum pump (918) is normally blocked to preventpassage of air through it from the upper part of the tank (911) when thevacuum pump (918) is at rest, or the pump tube (917) is provided with amanual or motorised, e.g. pressure-activated motorised, valve (930) (notshown), so that the pump tube (917) connecting to the vacuum pump (918)may be blocked to prevent such passage.

The operation of the apparatus (1) is similar to that of the apparatusin FIG. 1 mutatis mutandis.

In use of the apparatus (1), the valve (16) is opened to a collectionbag (not shown), and the T-valve (14) is turned to admit fluid from thefluid reservoir to the wound dressing through the fluid supply tube (7)and inlet pipe (6).

The pump (926) is started to nip the fluid recirculation tube (7) with•the peripheral rollers on its rotor (not shown) to apply a low positivepressure on the wound.

The vacuum pump (918) either acts as a valve since it is at rest, or thevalve (930) (not shown) is closed, so that the pump tube 917 is blockedto prevent passage of air through it from the upper part of the tank(911).

Irrigant pumped from the wound dressing (2) through the fluid offtaketube (10) is pumped through the lower part of the tank (911) up theoutlet tube (917) via the means for cleansing (17) to the bleed T-valve(16) into, e.g. a collection bag (not shown).

The peristaltic pump (926) acting on the fluid supply tube (7) upstreamof the dressing (2) is allowed to run until the apparatus is primedthroughout the whole length of the apparatus flow path and excess fluidis voided to waste via the bleed T-valve (16) into the collection bag.

The T-valve (14) is then turned to switch from supply to recirculation,i.e. is set to close the wound to the fluid reservoir (12) but to admitfluid into the wound from the fluid recirculation tube (13), and thebleed T-valve (16) is simultaneously closed.

The vacuum pump (918) is then activated, and, if the vacuum pump (918)does not act as a valve when at rest, the valve (930) in the pump tube917 is opened, to apply a low negative pressure to the wound.

The circulating fluid from the wound and the fluid reservoir (12) passesthrough the cleansing unit (17). Materials deleterious to wound healingare removed and the cleansed fluid, still containing materials that arebeneficial in promoting wound healing, is returned via the recirculationtube (13) to the wound bed.

The pressure feedback regulator (919) regulates the pressure at thewound and/or the tank (911).

If the amount of fluid in circulation becomes excessive, e.g. becausethe wound continues to exude heavily, the waste pump (914) may bestarted by the waste level feedback regulator (929) on the regulatorreceiving signals from the tank sensor with electrical line (930).

The recirculation of fluid may be continued as long as desired.

The vacuum pump (918) is then deactivated, and, if the vacuum pump (918)does not act as a valve when at rest, the valve (930) in the pump tube(917) is closed, and the bleed T-valve (16) is opened to air to relievethe low negative pressure in the tank (911) via the means for cleansing(17) and the outlet tube (917).

Switching between supply and recirculation is then reversed, by turningthe T-valve (14) to admit fluid from the •fluid reservoir to the wounddressing through the fluid supply tube (7) and inlet pipe (6).

The bleed valve (16) is left open, so that fresh fluid flushes therecirculating system. The running of the pump (918) may be continueduntil the apparatus is flushed, when it and the fluid recirculation isstopped.

The use of the apparatus of the present invention will now be describedby way of example only in the following Example:

Example

The combination of the removal by dialysis of materials deleterious towound healing CH202) by an enzyme (Catalase) retained in either a staticor a moving second phase and the use of a biological scaffold to promotetissue repair.

An apparatus of the present invention is constructed essentially as inFIG. 2, i.e. one in which the means for fluid cleansing is a two-phasesystem dialysis unit. In such an apparatus, an irrigant and/or woundexudate first phase from the wound recirculates through a first circuitand passes through the dialysis unit in contact across a selectivelypermeable dialysis membrane with a second fluid (dialysate) phase. Thedialysis unit is operated either with the two phases flowingcounter-current to each other or with a static second phase.

Hydrogen peroxide is produced in conditions of oxidative stressfollowing reduced blood flow and or the inflammatory response tobacterial contamination of wounds. It may be removed by the appropriateantagonists and/or degraders, which include enzymic or other inhibitors,such as peroxide degraders, e.g. catalase.

The first circuit consists of a chamber (Minucells organo-typicalgradient six-place chamber, holding tissue carriers) in whichhorizontally orientated 13 mm diameter discs of a normal diploid humanfibroblast containing tissue engineered dermal substitute (Dermagraft:Smith & Nephew) are retained in a two part support (MinnucellsMinusheets). Thus tissues present in the healing wound that mustsurvive, migrate and proliferate are represented by the fibroblast cellswithin the chamber.

To stimulate the growth of new tissue, a biodegradable scaffold in theform of a section of three-dimensional non-woven felt of a PGJ.\(poly(glycolic acid)) with a thickness of between 1-3 mm and 10-13 mm indiameter is laid over the cells within the chamber on the cover slips.

Nutrient medium (DMEM with 10% FCS with 1% Buffer All) to simulate woundexudate is pumped from a reservoir into the lower aspect of the chamberwhere it bathes the fibroblasts and is removed from the upper aspect ofthe chamber and returned to the reservoir. The chamber is constructedsuch that the only fluid path from the lower to the upper chamber isthrough the human fibroblast containing tissue-engineered dermalsubstitute. A measure of wound healing is the ability of the cellswithin the dermal substitute to increase in. thickness by migration andproliferation into the biodegradable scaffold.

For the moving second phase, the first circuit comprises, upstream ofthe wound chamber, a luer-fitting hollow fibre tangential membranedialysis unit (Spectrum® MicroKros® X14S-100-04N, 8 cm2 surface area,400 KD Mol. Wt. cut off,) through which a second cleansing circuitcontaining nutrient medium with between 5,000 and 50,000 units (μmolesH2O2 degraded per min at pH7, 25° C.) per ml of catalase (in a circuitwith a reservoir and total volume of between 5.0 ml and 20 ml) at a flowrate of between 0.5 ml min-1 and 5.0 ml min-1 is passed in a countercurrent direction. For the static second phase, a length of dialysistubing (Pierce Snake skin 68100 CG 493588, 10 KD cut off) containing thesame quantities and volume of catalase as for the moving second phase,is placed within the first circuit reservoir.

The pumps for the two circuits are peristaltic pumps acting on siliconetubing or equivalent. The internal diameter of the tubing is 1.0 mm. Atotal volume for the first circuit including the chamber and thereservoir at a number of values between 25 and 75 ml is used. The flowrates used are at a number of values between 0.5 ml/min 1 and 5.0 mlmin-1. The apparatus can be operated at atmospheric, positive ornegative pressures.

An experiment is conducted that simulates conditions not uncommon forhealing wounds whereby nutrient medium containing a material deleteriousto wound healing, namely hydrogen peroxide, is circulated over the cellswithin the wound chamber and a PGA biodegradable scaffold is placed onthe cells to simulate the wound bed.

Control experiments are also conducted where the three-dimensionalnon-woven felt biodegradable scaffold of a PGA (poly(glycolic acid)), orthe dialysis unit is omitted.

In controls where either the three-dimensional non-woven felt of a PGA(poly(glycolic acid)) with a thickness of between 1-3 mm, or the passageof the nutrient flow through the cleansing membrane dialysis unit isomitted, and the concentration of H202 lies between 5 and 20 mM,survival and migration and proliferation of the fibroblasts isinhibited.

However, when the nutrient medium flow in the first circuit is connectedinto the ends of the membrane dialysis unit through which a movingsecond phase cleansing circuit containing catalase (at theconcentrations and flow rates noted above) is passing in a countercurrent direction, or the flow is passed over a static second phasecatalase retained in a membrane and the PGA three-dimensional spongebiodegradable scaffold is present, the fibroblasts survive, migrate andproliferate into the scaffold.

The growth of new tissue in delayed healing or chronic wounds isfrequently limited by the slow rate of cell migration into the fibrinclot provisional matrix or in the formation of granulation tissue. Onestrategy to stimulate wound healing is to lay a biodegradable scaffoldor matrix on the surface of the wound but normally conditions found indelayed healing wounds limit the success of this approach.

The combination of the cleansing dialysis unit and the biodegradablescaffold employed in this apparatus enhances the cell responsesnecessary for wound healing.

What is claimed is:
 1. An apparatus for aspirating, irrigating and/orcleansing wounds, characterised in that it comprises a) a fluid flowpath, comprising i) a conformable wound dressing, having a backing layerwhich is capable of forming a relatively fluid-tight seal or closureover a wound and at least one inlet pipe for connection to a fluidsupply tube, which passes through and/or under the wound-facing face,and and at least one outlet pipe for connection to a fluid offtake tube,which passes through and/or under the wound-facing face, the point atwhich the or each inlet pipe and the or each outlet pipe passes throughand/or under the wound-facing face forming a relatively fluid-tight sealor closure over the wound, at least one inlet pipe being connected to afluid recirculation tube, and at least one outlet pipe being connectedto a fluid offtake tube: ii) a means for fluid cleansing having a leastone inlet port connected to a fluid offtake tube and at least one outletport connected to a fluid recirculation tube; and iii) a biodegradablescaffold located under the backing layer and configured to be placed incontact with a wound bed in use; b) a fluid reservoir connected by afluid supply tube to an integer of the flow path (optionally or asnecessary via means for flow switching between supply andrecirculation); c) a device for moving fluid through the wound dressingand means for fluid cleansing, and optionally or as necessary the fluidsupply tube; and e) means for bleeding the flowpath, such that fluid maybe supplied to fill the flowpath from the fluid reservoir via the fluidsupply tube (optionally or as necessary via the means for flowswitching) and recirculated by the device through the flow path.
 2. Anapparatus according to claim 1, characterised in that the biodegradablescaffold comprises a three-dimensional mesh, sponge or felt.
 3. Anapparatus according to claim 1, characterised in that the biodegradablescaffold comprises a poly(hydroxy acid) or ester thereof selected frompoly(glycolic acid), poly(L-lactic acid), poly(D-lactic acid) and estersthereof, or copolymers or blends thereof.
 4. An apparatus according toclaim 1, characterised in that the biodegradable scaffold comprises abiologically sourced biodegradable substantially protein based polymerselected from collagens, fibronectins, or fibrins, as whole molecules orderivatives thereof from proteolytic or chemical treatments, or blendsthereof; or a biodegradable substantially protein based polymer selectedfrom collagens, fibronectins, or fibrins, or fragments thereof, producedthrough recombinant DNA techniques, or blends thereof.
 5. An apparatusaccording to claim 1, characterised in that it comprises a means forfluid cleansing that is a single-phase system, in which the circulatingfluid from the wound passes through the means for fluid cleansing andmaterials—deleterious to wound healing are removed, without thecirculating fluid coming into direct or indirect contact with anotherfluid in the means for fluid cleansing.
 6. An apparatus according toclaim 1, characterised in that it comprises a means for fluid cleansingthat is a two-phase system, in which the circulating fluid from thewound passes through the means for fluid cleansing and materialsdeleterious to wound healing are removed, by the circulating fluidcoming into direct or indirect contact with another fluid in the meansfor fluid cleansing.
 7. An apparatus according to claim 3, characterisedin that in the means for fluid cleansing, the circulating fluid from thewound and the other fluid in the means for fluid cleansing are separatedby an integer which is selectively permeable to materials deleterious towound healing.
 8. An apparatus according to claim 3, characterised inthat in the means for fluid cleansing, the circulating fluid from thewound and the other fluid in the means for fluid cleansing are separatedby an integer which is not selectively permeable to materialsdeleterious to wound healing, and the other fluid comprises and/or is incontact with a material that removes materials deleterious to woundhealing.
 9. A conformable wound dressing assembly for use in anapparatus according to claim 1, characterised in that it comprises adressing as recited in claim 1 and a biodegradable scaffold.
 10. Amethod of treating wounds to promote wound healing using the apparatusfor aspirating, irrigating and/or cleansing wounds according to claim 1.